Introduce SignInResult/IdentityError/Describer

Follows Resource pattern (IdentityErrorDescriber.StringName, or
FormatStringName(arg1, arg2)
Also cleaned up optional services, by allowing null in constructor
SignInStatus -> SignInFailure and introduced SignInResult to make
SignInManager APIs consistent with IdentityResult (but no strings needed
for SignIn)
Fixes: #86, #176, #287 and #177

samples/IdentitySample.Mvc/Controllers/AccountController.cs

@@ -1,11 +1,10 @@
-using Microsoft.AspNet.Http;
-using Microsoft.AspNet.Identity;
-using Microsoft.AspNet.Mvc;
-using Microsoft.AspNet.Mvc.Rendering;
-using System.Linq;
+using System.Linq;
 using System.Security.Claims;
 using System.Security.Principal;
 using System.Threading.Tasks;
+using Microsoft.AspNet.Identity;
+using Microsoft.AspNet.Mvc;
+using Microsoft.AspNet.Mvc.Rendering;
 
 namespace IdentitySample.Models
 {
@@ -43,20 +42,23 @@ namespace IdentitySample.Models
             ViewBag.ReturnUrl = returnUrl;
             if (ModelState.IsValid)
             {
-                var signInStatus = await SignInManager.PasswordSignInAsync(model.UserName, model.Password, model.RememberMe, shouldLockout: false);
-                switch (signInStatus)
+                var result = await SignInManager.PasswordSignInAsync(model.UserName, model.Password, model.RememberMe, shouldLockout: false);
+                if (result.Succeeded)
                 {
-                    case SignInStatus.Success:
-                        return RedirectToLocal(returnUrl);
-                    case SignInStatus.LockedOut:
-                        ModelState.AddModelError("", "User is locked out, try again later.");
-                        return View(model);
-                    case SignInStatus.RequiresVerification:
-                        return RedirectToAction("SendCode", new { ReturnUrl = returnUrl, RememberMe = model.RememberMe });
-                    case SignInStatus.Failure:
-                    default:
-                        ModelState.AddModelError("", "Invalid username or password.");
-                        return View(model);
+                    return RedirectToLocal(returnUrl);
+                }
+                if (result.RequiresTwoFactor)
+                {
+                    return RedirectToAction("SendCode", new { ReturnUrl = returnUrl, RememberMe = model.RememberMe });
+                }
+                if (result.IsLockedOut)
+                {
+                    return View("Lockout");
+                }
+                else
+                {
+                    ModelState.AddModelError("", "Invalid username or password.");
+                    return View(model);
                 }
             }
 
@@ -143,22 +145,26 @@ namespace IdentitySample.Models
             // Sign in the user with this external login provider if the user already has a login
             var result = await SignInManager.ExternalLoginSignInAsync(info.LoginProvider, info.ProviderKey,
                 isPersistent: false);
-            switch (result)
+            if (result.Succeeded)
             {
-                case SignInStatus.Success:
-                    return RedirectToLocal(returnUrl);
-                case SignInStatus.LockedOut:
-                    return View("Lockout");
-                case SignInStatus.RequiresVerification:
-                    return RedirectToAction("SendCode", new { ReturnUrl = returnUrl });
-                case SignInStatus.Failure:
-                default:
-                    // If the user does not have an account, then prompt the user to create an account
-                    ViewBag.ReturnUrl = returnUrl;
-                    ViewBag.LoginProvider = info.LoginProvider;
-                    // REVIEW: handle case where email not in claims?
-                    var email = info.ExternalIdentity.FindFirstValue(ClaimTypes.Email);
-                    return View("ExternalLoginConfirmation", new ExternalLoginConfirmationViewModel { Email = email });
+                return RedirectToLocal(returnUrl);
+            }
+            if (result.RequiresTwoFactor)
+            {
+                return RedirectToAction("SendCode", new { ReturnUrl = returnUrl });
+            }
+            if (result.IsLockedOut)
+            {
+                return View("Lockout");
+            }
+            else
+            {
+                // If the user does not have an account, then prompt the user to create an account
+                ViewBag.ReturnUrl = returnUrl;
+                ViewBag.LoginProvider = info.LoginProvider;
+                // REVIEW: handle case where email not in claims?
+                var email = info.ExternalIdentity.FindFirstValue(ClaimTypes.Email);
+                return View("ExternalLoginConfirmation", new ExternalLoginConfirmationViewModel { Email = email });
             }
         }
 
@@ -380,15 +386,18 @@ namespace IdentitySample.Models
             }
 
             var result = await SignInManager.TwoFactorSignInAsync(model.Provider, model.Code, model.RememberMe, model.RememberBrowser);
-            switch (result)
+            if (result.Succeeded)
             {
-                case SignInStatus.Success:
-                    return RedirectToLocal(model.ReturnUrl);
-                case SignInStatus.LockedOut:
-                    return View("Lockout");
-                default:
-                    ModelState.AddModelError("", "Invalid code.");
-                    return View(model);
+                return RedirectToLocal(model.ReturnUrl);
+            }
+            if (result.IsLockedOut)
+            {
+                return View("Lockout");
+            }
+            else
+            {
+                ModelState.AddModelError("", "Invalid code.");
+                return View(model);
             }
         }
 
@@ -398,7 +407,7 @@ namespace IdentitySample.Models
         {
             foreach (var error in result.Errors)
             {
-                ModelState.AddModelError("", error);
+                ModelState.AddModelError("", error.Description);
             }
         }
 

samples/IdentitySample.Mvc/Controllers/ManageController.cs

@@ -346,7 +346,7 @@ namespace IdentitySample
         {
             foreach (var error in result.Errors)
             {
-                ModelState.AddModelError("", error);
+                ModelState.AddModelError("", error.Description);
             }
         }
 

src/Microsoft.AspNet.Identity/IdentityBuilder.cs

@@ -35,6 +35,12 @@ namespace Microsoft.AspNet.Identity
             return AddScoped(typeof(IRoleValidator<>).MakeGenericType(RoleType), typeof(T));
         }
 
+        public IdentityBuilder AddErrorDescriber<TDescriber>() where TDescriber : IdentityErrorDescriber
+        {
+            Services.AddScoped<IdentityErrorDescriber, TDescriber>();
+            return this;
+        }
+
         public IdentityBuilder AddPasswordValidator<T>() where T : class
         {
             return AddScoped(typeof(IPasswordValidator<>).MakeGenericType(UserType), typeof(T));

src/Microsoft.AspNet.Identity/IdentityError.cs

@@ -3,12 +3,9 @@
 
 namespace Microsoft.AspNet.Identity
 {
-    public enum SignInStatus
+    public class IdentityError
     {
-        Success,
-        LockedOut,
-        RequiresVerification,
-        NotAllowed,
-        Failure
+        public string Code { get; set; }
+        public string Description { get; set; }
     }
 }

src/Microsoft.AspNet.Identity/IdentityErrorDescriber.cs

@@ -0,0 +1,181 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.AspNet.Identity
+{
+    public class IdentityErrorDescriber
+    {
+        public static IdentityErrorDescriber Default = new IdentityErrorDescriber();
+
+        public virtual IdentityError DefaultError()
+        {
+            return new IdentityError
+            {
+                Code = nameof(DefaultError),
+                Description = Resources.DefaultError
+            };
+        }
+
+        public virtual IdentityError PasswordMismatch()
+        {
+            return new IdentityError
+            {
+                Code = nameof(PasswordMismatch),
+                Description = Resources.PasswordMismatch
+            };
+        }
+
+        public virtual IdentityError InvalidToken()
+        {
+            return new IdentityError
+            {
+                Code = nameof(InvalidToken),
+                Description = Resources.InvalidToken
+            };
+        }
+
+        public virtual IdentityError LoginAlreadyAssociated()
+        {
+            return new IdentityError
+            {
+                Code = nameof(LoginAlreadyAssociated),
+                Description = Resources.LoginAlreadyAssociated
+            };
+        }
+
+        public virtual IdentityError InvalidUserName(string name)
+        {
+            return new IdentityError
+            {
+                Code = nameof(InvalidUserName),
+                Description = Resources.FormatInvalidUserName(name)
+            };
+        }
+
+        public virtual IdentityError InvalidEmail(string email)
+        {
+            return new IdentityError
+            {
+                Code = nameof(InvalidEmail),
+                Description = Resources.FormatInvalidEmail(email)
+            };
+        }
+
+        public virtual IdentityError DuplicateUserName(string name)
+        {
+            return new IdentityError
+            {
+                Code = nameof(DuplicateUserName),
+                Description = Resources.FormatDuplicateUserName(name)
+            };
+        }
+
+        public virtual IdentityError DuplicateEmail(string email)
+        {
+            return new IdentityError
+            {
+                Code = nameof(DuplicateEmail),
+                Description = Resources.FormatDuplicateEmail(email)
+            };
+        }
+
+        public virtual IdentityError InvalidRoleName(string name)
+        {
+            return new IdentityError
+            {
+                Code = nameof(InvalidRoleName),
+                Description = Resources.FormatInvalidRoleName(name)
+            };
+        }
+
+        public virtual IdentityError DuplicateRoleName(string name)
+        {
+            return new IdentityError
+            {
+                Code = nameof(DuplicateRoleName),
+                Description = Resources.FormatDuplicateRoleName(name)
+            };
+        }
+
+        public virtual IdentityError UserAlreadyHasPassword()
+        {
+            return new IdentityError
+            {
+                Code = nameof(UserAlreadyHasPassword),
+                Description = Resources.UserAlreadyHasPassword
+            };
+        }
+
+        public virtual IdentityError UserLockoutNotEnabled()
+        {
+            return new IdentityError
+            {
+                Code = nameof(UserLockoutNotEnabled),
+                Description = Resources.UserLockoutNotEnabled
+            };
+        }
+
+        public virtual IdentityError UserAlreadyInRole(string role)
+        {
+            return new IdentityError
+            {
+                Code = nameof(UserAlreadyInRole),
+                Description = Resources.FormatUserAlreadyInRole(role)
+            };
+        }
+
+        public virtual IdentityError UserNotInRole(string role)
+        {
+            return new IdentityError
+            {
+                Code = nameof(UserNotInRole),
+                Description = Resources.FormatUserNotInRole(role)
+            };
+        }
+
+        public virtual IdentityError PasswordTooShort(int length)
+        {
+            return new IdentityError
+            {
+                Code = nameof(PasswordTooShort),
+                Description = Resources.FormatPasswordTooShort(length)
+            };
+        }
+
+        public virtual IdentityError PasswordRequiresNonLetterAndDigit()
+        {
+            return new IdentityError
+            {
+                Code = nameof(PasswordRequiresNonLetterAndDigit),
+                Description = Resources.PasswordRequiresNonLetterAndDigit
+            };
+        }
+
+        public virtual IdentityError PasswordRequiresDigit()
+        {
+            return new IdentityError
+            {
+                Code = nameof(PasswordRequiresDigit),
+                Description = Resources.PasswordRequiresDigit
+            };
+        }
+
+        public virtual IdentityError PasswordRequiresLower()
+        {
+            return new IdentityError
+            {
+                Code = nameof(PasswordRequiresLower),
+                Description = Resources.PasswordRequiresLower
+            };
+        }
+
+        public virtual IdentityError PasswordRequiresUpper()
+        {
+            return new IdentityError
+            {
+                Code = nameof(PasswordRequiresUpper),
+                Description = Resources.PasswordRequiresUpper
+            };
+        }
+    }
+}

src/Microsoft.AspNet.Identity/IdentityResult.cs

@@ -11,45 +11,19 @@ namespace Microsoft.AspNet.Identity
     /// </summary>
     public class IdentityResult
     {
-        private static readonly IdentityResult _success = new IdentityResult(true);
+        private static readonly IdentityResult _success = new IdentityResult { Succeeded = true };
 
-        /// <summary>
-        ///     Failure constructor that takes error messages
-        /// </summary>
-        /// <param name="errors"></param>
-        public IdentityResult(params string[] errors) : this((IEnumerable<string>)errors)
-        {
-        }
-
-        /// <summary>
-        ///     Failure constructor that takes error messages
-        /// </summary>
-        /// <param name="errors"></param>
-        public IdentityResult(IEnumerable<string> errors)
-        {
-            if (errors == null || !errors.Any())
-            {
-                errors = new[] { Resources.DefaultError };
-            }
-            Succeeded = false;
-            Errors = errors;
-        }
-
-        protected IdentityResult(bool success)
-        {
-            Succeeded = success;
-            Errors = new string[0];
-        }
+        private List<IdentityError> _errors = new List<IdentityError>();
 
         /// <summary>
         ///     True if the operation was successful
         /// </summary>
-        public bool Succeeded { get; private set; }
+        public bool Succeeded { get; protected set; }
 
         /// <summary>
         ///     List of errors
         /// </summary>
-        public IEnumerable<string> Errors { get; private set; }
+        public IEnumerable<IdentityError> Errors { get { return _errors; } }
 
         /// <summary>
         ///     Static success result
@@ -65,9 +39,14 @@ namespace Microsoft.AspNet.Identity
         /// </summary>
         /// <param name="errors"></param>
         /// <returns></returns>
-        public static IdentityResult Failed(params string[] errors)
+        public static IdentityResult Failed(params IdentityError[] errors)
         {
-            return new IdentityResult(errors);
+            var result = new IdentityResult { Succeeded = false };
+            if (errors != null)
+            {
+                result._errors.AddRange(errors);
+            }
+            return result;
         }
     }
 }

src/Microsoft.AspNet.Identity/IdentityServiceCollectionExtensions.cs

@@ -59,6 +59,8 @@ namespace Microsoft.Framework.DependencyInjection
             services.TryAdd(describe.Transient<IPasswordHasher<TUser>, PasswordHasher<TUser>>());
             services.TryAdd(describe.Transient<IUserNameNormalizer, UpperInvariantUserNameNormalizer>());
             services.TryAdd(describe.Transient<IRoleValidator<TRole>, RoleValidator<TRole>>());
+            // No interface for the error describer so we can add errors without rev'ing the interface
+            services.TryAdd(describe.Transient<IdentityErrorDescriber, IdentityErrorDescriber>());
             services.TryAdd(describe.Scoped<ISecurityStampValidator, SecurityStampValidator<TUser>>());
             services.TryAdd(describe.Scoped<IClaimsIdentityFactory<TUser>, ClaimsIdentityFactory<TUser, TRole>>());
             services.TryAdd(describe.Scoped<UserManager<TUser>, UserManager<TUser>>());

src/Microsoft.AspNet.Identity/PasswordHasher.cs

@@ -37,14 +37,11 @@ namespace Microsoft.AspNet.Identity
         ///     Constructs a PasswordHasher using the specified options
         /// </summary>
         /// <param name="options"></param>
-        public PasswordHasher(IOptions<PasswordHasherOptions> options)
+        public PasswordHasher(IOptions<PasswordHasherOptions> optionsAccessor = null)
         {
-            if (options == null)
-            {
-                throw new ArgumentNullException(nameof(options));
-            }
+            var options = optionsAccessor?.Options ?? new PasswordHasherOptions();
 
-            _compatibilityMode = options.Options.CompatibilityMode;
+            _compatibilityMode = options.CompatibilityMode;
             switch (_compatibilityMode)
             {
                 case PasswordHasherCompatibilityMode.IdentityV2:
@@ -52,7 +49,7 @@ namespace Microsoft.AspNet.Identity
                     break;
 
                 case PasswordHasherCompatibilityMode.IdentityV3:
-                    _iterCount = options.Options.IterationCount;
+                    _iterCount = options.IterationCount;
                     if (_iterCount < 1)
                     {
                         throw new InvalidOperationException(Resources.InvalidPasswordHasherIterationCount);
@@ -63,7 +60,7 @@ namespace Microsoft.AspNet.Identity
                     throw new InvalidOperationException(Resources.InvalidPasswordHasherCompatibilityMode);
             }
           
-            _rng = options.Options.Rng;
+            _rng = options.Rng;
         }
 
         // Compares two byte arrays for equality. The method is specifically written so that the loop is not optimized.

src/Microsoft.AspNet.Identity/PasswordValidator.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
@@ -15,6 +14,13 @@ namespace Microsoft.AspNet.Identity
     /// </summary>
     public class PasswordValidator<TUser> : IPasswordValidator<TUser> where TUser : class
     {
+        public PasswordValidator(IdentityErrorDescriber errors = null)
+        {
+            Describer = errors ?? new IdentityErrorDescriber();
+        }
+
+        public IdentityErrorDescriber Describer { get; private set; }
+
         /// <summary>
         ///     Ensures that the password is of the required length and meets the configured requirements
         /// </summary>
@@ -33,33 +39,32 @@ namespace Microsoft.AspNet.Identity
             {
                 throw new ArgumentNullException("manager");
             }
-            var errors = new List<string>();
+            var errors = new List<IdentityError>();
             var options = manager.Options.Password;
             if (string.IsNullOrWhiteSpace(password) || password.Length < options.RequiredLength)
             {
-                errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.PasswordTooShort, 
-                    options.RequiredLength));
+                errors.Add(Describer.PasswordTooShort(options.RequiredLength));
             }
             if (options.RequireNonLetterOrDigit && password.All(IsLetterOrDigit))
             {
-                errors.Add(Resources.PasswordRequireNonLetterOrDigit);
+                errors.Add(Describer.PasswordRequiresNonLetterAndDigit());
             }
             if (options.RequireDigit && !password.Any(IsDigit))
             {
-                errors.Add(Resources.PasswordRequireDigit);
+                errors.Add(Describer.PasswordRequiresDigit());
             }
             if (options.RequireLowercase && !password.Any(IsLower))
             {
-                errors.Add(Resources.PasswordRequireLower);
+                errors.Add(Describer.PasswordRequiresLower());
             }
             if (options.RequireUppercase && !password.Any(IsUpper))
             {
-                errors.Add(Resources.PasswordRequireUpper);
+                errors.Add(Describer.PasswordRequiresUpper());
             }
             return
                 Task.FromResult(errors.Count == 0
                     ? IdentityResult.Success
-                    : IdentityResult.Failed(String.Join(" ", errors)));
+                    : IdentityResult.Failed(errors.ToArray()));
         }
 
         /// <summary>

src/Microsoft.AspNet.Identity/Properties/Resources.Designer.cs

@@ -139,35 +139,35 @@ namespace Microsoft.AspNet.Identity
         }
 
         /// <summary>
-        /// Name {0} is already taken.
+        /// Role Name '{0}' is already taken.
         /// </summary>
-        internal static string DuplicateName
+        internal static string DuplicateRoleName
         {
-            get { return GetString("DuplicateName"); }
+            get { return GetString("DuplicateRoleName"); }
         }
 
         /// <summary>
-        /// Name {0} is already taken.
+        /// Role Name '{0}' is already taken.
         /// </summary>
-        internal static string FormatDuplicateName(object p0)
+        internal static string FormatDuplicateRoleName(object p0)
         {
-            return string.Format(CultureInfo.CurrentCulture, GetString("DuplicateName"), p0);
+            return string.Format(CultureInfo.CurrentCulture, GetString("DuplicateRoleName"), p0);
         }
 
         /// <summary>
-        /// A user with that external login already exists.
+        /// UserName '{0}' is already taken.
         /// </summary>
-        internal static string ExternalLoginExists
+        internal static string DuplicateUserName
         {
-            get { return GetString("ExternalLoginExists"); }
+            get { return GetString("DuplicateUserName"); }
         }
 
         /// <summary>
-        /// A user with that external login already exists.
+        /// UserName '{0}' is already taken.
         /// </summary>
-        internal static string FormatExternalLoginExists()
+        internal static string FormatDuplicateUserName(object p0)
         {
-            return GetString("ExternalLoginExists");
+            return string.Format(CultureInfo.CurrentCulture, GetString("DuplicateUserName"), p0);
         }
 
         /// <summary>
@@ -218,6 +218,22 @@ namespace Microsoft.AspNet.Identity
             return GetString("InvalidPasswordHasherIterationCount");
         }
 
+        /// <summary>
+        /// Role name '{0}' is invalid.
+        /// </summary>
+        internal static string InvalidRoleName
+        {
+            get { return GetString("InvalidRoleName"); }
+        }
+
+        /// <summary>
+        /// Role name '{0}' is invalid.
+        /// </summary>
+        internal static string FormatInvalidRoleName(object p0)
+        {
+            return string.Format(CultureInfo.CurrentCulture, GetString("InvalidRoleName"), p0);
+        }
+
         /// <summary>
         /// Invalid token.
         /// </summary>
@@ -235,7 +251,7 @@ namespace Microsoft.AspNet.Identity
         }
 
         /// <summary>
-        /// User name {0} is invalid, can only contain letters or digits.
+        /// User name '{0}' is invalid, can only contain letters or digits.
         /// </summary>
         internal static string InvalidUserName
         {
@@ -243,7 +259,7 @@ namespace Microsoft.AspNet.Identity
         }
 
         /// <summary>
-        /// User name {0} is invalid, can only contain letters or digits.
+        /// User name '{0}' is invalid, can only contain letters or digits.
         /// </summary>
         internal static string FormatInvalidUserName(object p0)
         {
@@ -251,19 +267,19 @@ namespace Microsoft.AspNet.Identity
         }
 
         /// <summary>
-        /// Lockout is not enabled for this user.
+        /// A user with this login already exists.
         /// </summary>
-        internal static string LockoutNotEnabled
+        internal static string LoginAlreadyAssociated
         {
-            get { return GetString("LockoutNotEnabled"); }
+            get { return GetString("LoginAlreadyAssociated"); }
         }
 
         /// <summary>
-        /// Lockout is not enabled for this user.
+        /// A user with this login already exists.
         /// </summary>
-        internal static string FormatLockoutNotEnabled()
+        internal static string FormatLoginAlreadyAssociated()
         {
-            return GetString("LockoutNotEnabled");
+            return GetString("LoginAlreadyAssociated");
         }
 
         /// <summary>
@@ -317,65 +333,65 @@ namespace Microsoft.AspNet.Identity
         /// <summary>
         /// Passwords must have at least one digit ('0'-'9').
         /// </summary>
-        internal static string PasswordRequireDigit
+        internal static string PasswordRequiresDigit
         {
-            get { return GetString("PasswordRequireDigit"); }
+            get { return GetString("PasswordRequiresDigit"); }
         }
 
         /// <summary>
         /// Passwords must have at least one digit ('0'-'9').
         /// </summary>
-        internal static string FormatPasswordRequireDigit()
+        internal static string FormatPasswordRequiresDigit()
         {
-            return GetString("PasswordRequireDigit");
+            return GetString("PasswordRequiresDigit");
         }
 
         /// <summary>
         /// Passwords must have at least one lowercase ('a'-'z').
         /// </summary>
-        internal static string PasswordRequireLower
+        internal static string PasswordRequiresLower
         {
-            get { return GetString("PasswordRequireLower"); }
+            get { return GetString("PasswordRequiresLower"); }
         }
 
         /// <summary>
         /// Passwords must have at least one lowercase ('a'-'z').
         /// </summary>
-        internal static string FormatPasswordRequireLower()
+        internal static string FormatPasswordRequiresLower()
         {
-            return GetString("PasswordRequireLower");
+            return GetString("PasswordRequiresLower");
         }
 
         /// <summary>
         /// Passwords must have at least one non letter and non digit character.
         /// </summary>
-        internal static string PasswordRequireNonLetterOrDigit
+        internal static string PasswordRequiresNonLetterAndDigit
         {
-            get { return GetString("PasswordRequireNonLetterOrDigit"); }
+            get { return GetString("PasswordRequiresNonLetterAndDigit"); }
         }
 
         /// <summary>
         /// Passwords must have at least one non letter and non digit character.
         /// </summary>
-        internal static string FormatPasswordRequireNonLetterOrDigit()
+        internal static string FormatPasswordRequiresNonLetterAndDigit()
         {
-            return GetString("PasswordRequireNonLetterOrDigit");
+            return GetString("PasswordRequiresNonLetterAndDigit");
         }
 
         /// <summary>
         /// Passwords must have at least one uppercase ('A'-'Z').
         /// </summary>
-        internal static string PasswordRequireUpper
+        internal static string PasswordRequiresUpper
         {
-            get { return GetString("PasswordRequireUpper"); }
+            get { return GetString("PasswordRequiresUpper"); }
         }
 
         /// <summary>
         /// Passwords must have at least one uppercase ('A'-'Z').
         /// </summary>
-        internal static string FormatPasswordRequireUpper()
+        internal static string FormatPasswordRequiresUpper()
         {
-            return GetString("PasswordRequireUpper");
+            return GetString("PasswordRequiresUpper");
         }
 
         /// <summary>
@@ -651,7 +667,7 @@ namespace Microsoft.AspNet.Identity
         }
 
         /// <summary>
-        /// User already in role.
+        /// User already in role '{0}'.
         /// </summary>
         internal static string UserAlreadyInRole
         {
@@ -659,11 +675,43 @@ namespace Microsoft.AspNet.Identity
         }
 
         /// <summary>
-        /// User already in role.
+        /// User already in role '{0}'.
         /// </summary>
-        internal static string FormatUserAlreadyInRole()
+        internal static string FormatUserAlreadyInRole(object p0)
         {
-            return GetString("UserAlreadyInRole");
+            return string.Format(CultureInfo.CurrentCulture, GetString("UserAlreadyInRole"), p0);
+        }
+
+        /// <summary>
+        /// User is locked out.
+        /// </summary>
+        internal static string UserLockedOut
+        {
+            get { return GetString("UserLockedOut"); }
+        }
+
+        /// <summary>
+        /// User is locked out.
+        /// </summary>
+        internal static string FormatUserLockedOut()
+        {
+            return GetString("UserLockedOut");
+        }
+
+        /// <summary>
+        /// Lockout is not enabled for this user.
+        /// </summary>
+        internal static string UserLockoutNotEnabled
+        {
+            get { return GetString("UserLockoutNotEnabled"); }
+        }
+
+        /// <summary>
+        /// Lockout is not enabled for this user.
+        /// </summary>
+        internal static string FormatUserLockoutNotEnabled()
+        {
+            return GetString("UserLockoutNotEnabled");
         }
 
         /// <summary>
@@ -683,7 +731,7 @@ namespace Microsoft.AspNet.Identity
         }
 
         /// <summary>
-        /// User is not in role.
+        /// User is not in role '{0}'.
         /// </summary>
         internal static string UserNotInRole
         {
@@ -691,11 +739,11 @@ namespace Microsoft.AspNet.Identity
         }
 
         /// <summary>
-        /// User is not in role.
+        /// User is not in role '{0}'.
         /// </summary>
-        internal static string FormatUserNotInRole()
+        internal static string FormatUserNotInRole(object p0)
         {
-            return GetString("UserNotInRole");
+            return string.Format(CultureInfo.CurrentCulture, GetString("UserNotInRole"), p0);
         }
 
         private static string GetString(string name, params string[] formatterNames)

src/Microsoft.AspNet.Identity/Resources.resx

@@ -149,13 +149,13 @@
     <value>Email '{0}' is already taken.</value>
     <comment>error for duplicate emails</comment>
   </data>
-  <data name="DuplicateName" xml:space="preserve">
-    <value>Name {0} is already taken.</value>
+  <data name="DuplicateRoleName" xml:space="preserve">
+    <value>Role Name '{0}' is already taken.</value>
     <comment>error for duplicate usernames</comment>
   </data>
-  <data name="ExternalLoginExists" xml:space="preserve">
-    <value>A user with that external login already exists.</value>
-    <comment>Error when a login already linked</comment>
+  <data name="DuplicateUserName" xml:space="preserve">
+    <value>UserName '{0}' is already taken.</value>
+    <comment>error for duplicate usernames</comment>
   </data>
   <data name="InvalidEmail" xml:space="preserve">
     <value>Email '{0}' is invalid.</value>
@@ -169,17 +169,21 @@
     <value>The iteration count must be a positive integer.</value>
     <comment>Error when the iteration count is &lt; 1.</comment>
   </data>
+  <data name="InvalidRoleName" xml:space="preserve">
+    <value>Role name '{0}' is invalid.</value>
+    <comment>error for invalid role names</comment>
+  </data>
   <data name="InvalidToken" xml:space="preserve">
     <value>Invalid token.</value>
     <comment>Error when a token is not recognized</comment>
   </data>
   <data name="InvalidUserName" xml:space="preserve">
-    <value>User name {0} is invalid, can only contain letters or digits.</value>
+    <value>User name '{0}' is invalid, can only contain letters or digits.</value>
     <comment>usernames can only contain letters or digits</comment>
   </data>
-  <data name="LockoutNotEnabled" xml:space="preserve">
-    <value>Lockout is not enabled for this user.</value>
-    <comment>error when lockout is not enabled</comment>
+  <data name="LoginAlreadyAssociated" xml:space="preserve">
+    <value>A user with this login already exists.</value>
+    <comment>Error when a login already linked</comment>
   </data>
   <data name="NoMessageProvider" xml:space="preserve">
     <value>No IUserMessageProvider named '{0}' is registered.</value>
@@ -193,19 +197,19 @@
     <value>Incorrect password.</value>
     <comment>Error when a password doesn't match</comment>
   </data>
-  <data name="PasswordRequireDigit" xml:space="preserve">
+  <data name="PasswordRequiresDigit" xml:space="preserve">
     <value>Passwords must have at least one digit ('0'-'9').</value>
     <comment>Error when passwords do not have a digit</comment>
   </data>
-  <data name="PasswordRequireLower" xml:space="preserve">
+  <data name="PasswordRequiresLower" xml:space="preserve">
     <value>Passwords must have at least one lowercase ('a'-'z').</value>
     <comment>Error when passwords do not have a lowercase letter</comment>
   </data>
-  <data name="PasswordRequireNonLetterOrDigit" xml:space="preserve">
+  <data name="PasswordRequiresNonLetterAndDigit" xml:space="preserve">
     <value>Passwords must have at least one non letter and non digit character.</value>
     <comment>Error when password does not have enough letter or digit characters</comment>
   </data>
-  <data name="PasswordRequireUpper" xml:space="preserve">
+  <data name="PasswordRequiresUpper" xml:space="preserve">
     <value>Passwords must have at least one uppercase ('A'-'Z').</value>
     <comment>Error when passwords do not have an uppercase letter</comment>
   </data>
@@ -213,10 +217,6 @@
     <value>Passwords must be at least {0} characters.</value>
     <comment>Error message for passwords that are too short</comment>
   </data>
-  <data name="PropertyTooShort" xml:space="preserve">
-    <value>{0} cannot be null or empty.</value>
-    <comment>error for empty or null usernames</comment>
-  </data>
   <data name="RoleNotFound" xml:space="preserve">
     <value>Role {0} does not exist.</value>
     <comment>error when a role does not exist</comment>
@@ -278,15 +278,23 @@
     <comment>error when AddPasswordAsync called when a user already has a password</comment>
   </data>
   <data name="UserAlreadyInRole" xml:space="preserve">
-    <value>User already in role.</value>
+    <value>User already in role '{0}'.</value>
     <comment>Error when a user is already in a role</comment>
   </data>
+  <data name="UserLockedOut" xml:space="preserve">
+    <value>User is locked out.</value>
+    <comment>Error when a user is locked out</comment>
+  </data>
+  <data name="UserLockoutNotEnabled" xml:space="preserve">
+    <value>Lockout is not enabled for this user.</value>
+    <comment>error when lockout is not enabled</comment>
+  </data>
   <data name="UserNameNotFound" xml:space="preserve">
     <value>User {0} does not exist.</value>
     <comment>error when a user does not exist</comment>
   </data>
   <data name="UserNotInRole" xml:space="preserve">
-    <value>User is not in role.</value>
+    <value>User is not in role '{0}'.</value>
     <comment>Error when a user is not in the role</comment>
   </data>
 </root>

src/Microsoft.AspNet.Identity/RoleManager.cs

@@ -24,13 +24,16 @@ namespace Microsoft.AspNet.Identity
         /// </summary>
         /// <param name="store">The IRoleStore commits changes via the UpdateAsync/CreateAsync methods</param>
         /// <param name="roleValidator"></param>
-        public RoleManager(IRoleStore<TRole> store, IEnumerable<IRoleValidator<TRole>> roleValidators)
+        public RoleManager(IRoleStore<TRole> store, 
+            IEnumerable<IRoleValidator<TRole>> roleValidators = null,
+            IdentityErrorDescriber errors = null)
         {
             if (store == null)
             {
                 throw new ArgumentNullException("store");
             }
             Store = store;
+            ErrorDescriber = errors ?? new IdentityErrorDescriber();
 
             if (roleValidators != null)
             {
@@ -51,6 +54,11 @@ namespace Microsoft.AspNet.Identity
         /// </summary>
         public IList<IRoleValidator<TRole>> RoleValidators { get; } = new List<IRoleValidator<TRole>>();
 
+        /// <summary>
+        ///     Used to generate public API error messages
+        /// </summary>
+        public IdentityErrorDescriber ErrorDescriber { get; set; }
+
         /// <summary>
         ///     Returns an IQueryable of roles if the store is an IQueryableRoleStore
         /// </summary>
@@ -102,7 +110,7 @@ namespace Microsoft.AspNet.Identity
 
         private async Task<IdentityResult> ValidateRoleInternal(TRole role, CancellationToken cancellationToken)
         {
-            var errors = new List<string>();
+            var errors = new List<IdentityError>();
             foreach (var v in RoleValidators)
             {
                 var result = await v.ValidateAsync(this, role, cancellationToken);

src/Microsoft.AspNet.Identity/RoleValidator.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -15,6 +14,13 @@ namespace Microsoft.AspNet.Identity
     /// <typeparam name="TRole"></typeparam>
     public class RoleValidator<TRole> : IRoleValidator<TRole> where TRole : class
     {
+        public RoleValidator(IdentityErrorDescriber errors = null)
+        {
+            Describer = errors ?? new IdentityErrorDescriber();
+        }
+
+        private IdentityErrorDescriber Describer { get; set; }
+
         /// <summary>
         ///     Validates a role before saving
         /// </summary>
@@ -33,7 +39,7 @@ namespace Microsoft.AspNet.Identity
             {
                 throw new ArgumentNullException("role");
             }
-            var errors = new List<string>();
+            var errors = new List<IdentityError>();
             await ValidateRoleName(manager, role, errors);
             if (errors.Count > 0)
             {
@@ -42,13 +48,13 @@ namespace Microsoft.AspNet.Identity
             return IdentityResult.Success;
         }
 
-        private static async Task ValidateRoleName(RoleManager<TRole> manager, TRole role,
-            ICollection<string> errors)
+        private async Task ValidateRoleName(RoleManager<TRole> manager, TRole role,
+            ICollection<IdentityError> errors)
         {
             var roleName = await manager.GetRoleNameAsync(role);
             if (string.IsNullOrWhiteSpace(roleName))
             {
-                errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.PropertyTooShort, "Name"));
+                errors.Add(Describer.InvalidRoleName(roleName));
             }
             else
             {
@@ -56,7 +62,7 @@ namespace Microsoft.AspNet.Identity
                 if (owner != null && 
                     !string.Equals(await manager.GetRoleIdAsync(owner), await manager.GetRoleIdAsync(role)))
                 {
-                    errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.DuplicateName, roleName));
+                    errors.Add(Describer.DuplicateRoleName(roleName));
                 }
             }
         }

src/Microsoft.AspNet.Identity/SignInManager.cs

@@ -21,8 +21,10 @@ namespace Microsoft.AspNet.Identity
     /// <typeparam name="TUser"></typeparam>
     public class SignInManager<TUser> where TUser : class
     {
-        public SignInManager(UserManager<TUser> userManager, IContextAccessor<HttpContext> contextAccessor, 
-            IClaimsIdentityFactory<TUser> claimsFactory, IOptions<IdentityOptions> optionsAccessor)
+        public SignInManager(UserManager<TUser> userManager, 
+            IContextAccessor<HttpContext> contextAccessor, 
+            IClaimsIdentityFactory<TUser> claimsFactory, 
+            IOptions<IdentityOptions> optionsAccessor = null)
         {
             if (userManager == null)
             {
@@ -36,14 +38,10 @@ namespace Microsoft.AspNet.Identity
             {
                 throw new ArgumentNullException(nameof(claimsFactory));
             }
-            if (optionsAccessor == null || optionsAccessor.Options == null)
-            {
-                throw new ArgumentNullException(nameof(optionsAccessor));
-            }
             UserManager = userManager;
             Context = contextAccessor.Value;
             ClaimsFactory = claimsFactory;
-            Options = optionsAccessor.Options;
+            Options = optionsAccessor?.Options ?? new IdentityOptions();
         }
 
         public UserManager<TUser> UserManager { get; private set; }
@@ -96,15 +94,15 @@ namespace Microsoft.AspNet.Identity
             return UserManager.SupportsUserLockout && await UserManager.IsLockedOutAsync(user, token);
         }
 
-        private async Task<SignInStatus?> PreSignInCheck(TUser user, CancellationToken token)
+        private async Task<SignInResult> PreSignInCheck(TUser user, CancellationToken token)
         {
             if (!await CanSignInAsync(user, token))
             {
-                return SignInStatus.NotAllowed;
+                return SignInResult.NotAllowed;
             }
             if (await IsLockedOut(user, token))
             {
-                return SignInStatus.LockedOut;
+                return SignInResult.LockedOut;
             }
             return null;
         }
@@ -141,13 +139,21 @@ namespace Microsoft.AspNet.Identity
             return null;
         }
 
-        public virtual async Task<SignInStatus> PasswordSignInAsync(TUser user, string password,
+        public virtual async Task<SignInResult> PasswordSignInAsync(TUser user, string password, 
             bool isPersistent, bool shouldLockout, CancellationToken cancellationToken = default(CancellationToken))
         {
+            if (user == null)
+            {
+                throw new ArgumentNullException(nameof(user));
+            }
             var error = await PreSignInCheck(user, cancellationToken);
             if (error != null)
             {
-                return error.Value;
+                return error;
+            }
+            if (await IsLockedOut(user, cancellationToken))
+            {
+                return SignInResult.LockedOut;
             }
             if (await UserManager.CheckPasswordAsync(user, password, cancellationToken))
             {
@@ -160,19 +166,19 @@ namespace Microsoft.AspNet.Identity
                 await UserManager.AccessFailedAsync(user, cancellationToken);
                 if (await UserManager.IsLockedOutAsync(user, cancellationToken))
                 {
-                    return SignInStatus.LockedOut;
+                    return SignInResult.LockedOut;
                 }
             }
-            return SignInStatus.Failure;
+            return SignInResult.Failed;
         }
 
-        public virtual async Task<SignInStatus> PasswordSignInAsync(string userName, string password, 
+        public virtual async Task<SignInResult> PasswordSignInAsync(string userName, string password,
             bool isPersistent, bool shouldLockout, CancellationToken cancellationToken = default(CancellationToken))
         {
             var user = await UserManager.FindByNameAsync(userName, cancellationToken);
             if (user == null)
             {
-                return SignInStatus.Failure;
+                return SignInResult.Failed;
             }
             return await PasswordSignInAsync(user, password, isPersistent, shouldLockout, cancellationToken);
         }
@@ -207,7 +213,6 @@ namespace Microsoft.AspNet.Identity
                 return false;
             }
             var token = await UserManager.GenerateTwoFactorTokenAsync(user, provider, cancellationToken);
-            // See IdentityConfig.cs to plug in Email/SMS services to actually send the code
             await UserManager.NotifyTwoFactorTokenAsync(user, provider, token, cancellationToken);
             return true;
         }
@@ -236,23 +241,23 @@ namespace Microsoft.AspNet.Identity
             return Task.FromResult(0);
         }
 
-        public virtual async Task<SignInStatus> TwoFactorSignInAsync(string provider, string code, bool isPersistent, 
+        public virtual async Task<SignInResult> TwoFactorSignInAsync(string provider, string code, bool isPersistent,
             bool rememberClient, CancellationToken cancellationToken = default(CancellationToken))
         {
             var twoFactorInfo = await RetrieveTwoFactorInfoAsync(cancellationToken);
             if (twoFactorInfo == null || twoFactorInfo.UserId == null)
             {
-                return SignInStatus.Failure;
+                return SignInResult.Failed;
             }
             var user = await UserManager.FindByIdAsync(twoFactorInfo.UserId, cancellationToken);
             if (user == null)
             {
-                return SignInStatus.Failure;
+                return SignInResult.Failed;
             }
             var error = await PreSignInCheck(user, cancellationToken);
             if (error != null)
             {
-                return error.Value;
+                return error;
             }
             if (await UserManager.VerifyTwoFactorTokenAsync(user, provider, code, cancellationToken))
             {
@@ -268,11 +273,13 @@ namespace Microsoft.AspNet.Identity
                 {
                     await RememberTwoFactorClientAsync(user, cancellationToken);
                 }
-                return SignInStatus.Success;
+                await UserManager.ResetAccessFailedCountAsync(user, cancellationToken);
+                await SignInAsync(user, isPersistent);
+                return SignInResult.Success;
             }
             // If the token is incorrect, record the failure which also may cause the user to be locked out
             await UserManager.AccessFailedAsync(user, cancellationToken);
-            return SignInStatus.Failure;
+            return SignInResult.Failed;
         }
 
         /// <summary>
@@ -292,18 +299,18 @@ namespace Microsoft.AspNet.Identity
             return await UserManager.FindByIdAsync(info.UserId, cancellationToken);
         }
 
-        public virtual async Task<SignInStatus> ExternalLoginSignInAsync(string loginProvider, string providerKey, bool isPersistent,
+        public async Task<SignInResult> ExternalLoginSignInAsync(string loginProvider, string providerKey, bool isPersistent,
             CancellationToken cancellationToken = default(CancellationToken))
         {
             var user = await UserManager.FindByLoginAsync(loginProvider, providerKey, cancellationToken);
             if (user == null)
             {
-                return SignInStatus.Failure;
+                return SignInResult.Failed;
             }
             var error = await PreSignInCheck(user, cancellationToken);
             if (error != null)
             {
-                return error.Value;
+                return error;
             }
             return await SignInOrTwoFactorAsync(user, isPersistent, cancellationToken, loginProvider);
         }
@@ -358,7 +365,7 @@ namespace Microsoft.AspNet.Identity
             return properties;
         }
 
-        private async Task<SignInStatus> SignInOrTwoFactorAsync(TUser user, bool isPersistent,
+        private async Task<SignInResult> SignInOrTwoFactorAsync(TUser user, bool isPersistent,
             CancellationToken cancellationToken, string loginProvider = null)
         {
             if (UserManager.SupportsUserTwoFactor && 
@@ -370,7 +377,7 @@ namespace Microsoft.AspNet.Identity
                     // Store the userId for use after two factor check
                     var userId = await UserManager.GetUserIdAsync(user, cancellationToken);
                     Context.Response.SignIn(StoreTwoFactorInfo(userId, loginProvider));
-                    return SignInStatus.RequiresVerification;
+                    return SignInResult.TwoFactorRequired;
                 }
             }
             // Cleanup external cookie
@@ -379,7 +386,7 @@ namespace Microsoft.AspNet.Identity
                 Context.Response.SignOut(IdentityOptions.ExternalCookieAuthenticationType);
             }
             await SignInAsync(user, isPersistent, loginProvider, cancellationToken);
-            return SignInStatus.Success;
+            return SignInResult.Success;
         }
 
         private async Task<TwoFactorAuthenticationInfo> RetrieveTwoFactorInfoAsync(CancellationToken cancellationToken)

src/Microsoft.AspNet.Identity/SignInResult.cs

@@ -0,0 +1,84 @@
+// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.AspNet.Identity
+{
+    /// <summary>
+    ///     Represents the result of an sign in operation
+    /// </summary>
+    public class SignInResult
+    {
+        private static readonly SignInResult _success = new SignInResult { Succeeded = true };
+        private static readonly SignInResult _failed = new SignInResult();
+        private static readonly SignInResult _lockedOut = new SignInResult { IsLockedOut = true };
+        private static readonly SignInResult _notAllowed = new SignInResult { IsNotAllowed = true };
+        private static readonly SignInResult _twoFactorRequired = new SignInResult { RequiresTwoFactor = true };
+
+        /// <summary>
+        ///     True if the operation was successful
+        /// </summary>
+        public bool Succeeded { get; protected set; }
+
+        /// <summary>
+        ///     True if the user is locked out
+        /// </summary>
+        public bool IsLockedOut { get; protected set; }
+
+        /// <summary>
+        ///     True if the user is not allowed to sign in
+        /// </summary>
+        public bool IsNotAllowed { get; protected set; }
+
+        /// <summary>
+        ///     True if the sign in requires two factor
+        /// </summary>
+        public bool RequiresTwoFactor { get; protected set; }
+
+        /// <summary>
+        ///     Static success result
+        /// </summary>
+        /// <returns></returns>
+        public static SignInResult Success
+        {
+            get { return _success; }
+        }
+
+        /// <summary>
+        ///     Static failure result
+        /// </summary>
+        /// <returns></returns>
+        public static SignInResult Failed
+        {
+            get { return _failed; }
+        }
+
+        /// <summary>
+        ///     Static locked out result
+        /// </summary>
+        /// <returns></returns>
+        public static SignInResult LockedOut
+        {
+            get { return _lockedOut; }
+        }
+
+        /// <summary>
+        ///     Static not allowed result
+        /// </summary>
+        /// <returns></returns>
+        public static SignInResult NotAllowed
+        {
+            get { return _notAllowed; }
+        }
+
+        /// <summary>
+        ///     Static two factor required result
+        /// </summary>
+        /// <returns></returns>
+        public static SignInResult TwoFactorRequired
+        {
+            get { return _twoFactorRequired; }
+        }
+
+
+    }
+}

src/Microsoft.AspNet.Identity/UserManager.cs

@@ -39,30 +39,24 @@ namespace Microsoft.AspNet.Identity
         /// <param name="passwordValidator"></param>
         /// <param name="claimsIdentityFactory"></param>
         public UserManager(IUserStore<TUser> store, 
-            IOptions<IdentityOptions> optionsAccessor,
-            IPasswordHasher<TUser> passwordHasher, 
-            IEnumerable<IUserValidator<TUser>> userValidators,
-            IEnumerable<IPasswordValidator<TUser>> passwordValidators, 
-            IUserNameNormalizer userNameNormalizer,
-            IEnumerable<IUserTokenProvider<TUser>> tokenProviders, 
-            IEnumerable<IIdentityMessageProvider> msgProviders)
+            IOptions<IdentityOptions> optionsAccessor = null,
+            IPasswordHasher<TUser> passwordHasher = null, 
+            IEnumerable<IUserValidator<TUser>> userValidators = null,
+            IEnumerable<IPasswordValidator<TUser>> passwordValidators = null, 
+            IUserNameNormalizer userNameNormalizer = null,
+            IdentityErrorDescriber errors = null,
+            IEnumerable<IUserTokenProvider<TUser>> tokenProviders = null, 
+            IEnumerable<IIdentityMessageProvider> msgProviders = null)
         {
             if (store == null)
             {
                 throw new ArgumentNullException(nameof(store));
             }
-            if (optionsAccessor == null || optionsAccessor.Options == null)
-            {
-                throw new ArgumentNullException(nameof(optionsAccessor));
-            }
-            if (passwordHasher == null)
-            {
-                throw new ArgumentNullException(nameof(passwordHasher));
-            }
             Store = store;
-            Options = optionsAccessor.Options;
-            PasswordHasher = passwordHasher;
-            UserNameNormalizer = userNameNormalizer;
+            Options = optionsAccessor?.Options ?? new IdentityOptions();
+            PasswordHasher = passwordHasher ?? new PasswordHasher<TUser>();
+            UserNameNormalizer = userNameNormalizer ?? new UpperInvariantUserNameNormalizer();
+            ErrorDescriber = errors ?? new IdentityErrorDescriber();
             if (userValidators != null)
             {
                 foreach (var v in userValidators)
@@ -136,6 +130,11 @@ namespace Microsoft.AspNet.Identity
         /// </summary>
         public IUserNameNormalizer UserNameNormalizer { get; set; }
 
+        /// <summary>
+        ///     Used to generate public API error messages
+        /// </summary>
+        public IdentityErrorDescriber ErrorDescriber { get; set; }
+
         public IdentityOptions Options
         {
             get
@@ -301,7 +300,7 @@ namespace Microsoft.AspNet.Identity
 
         private async Task<IdentityResult> ValidateUserInternal(TUser user, CancellationToken cancellationToken)
         {
-            var errors = new List<string>();
+            var errors = new List<IdentityError>();
             foreach (var v in UserValidators)
             {
                 var result = await v.ValidateAsync(this, user, cancellationToken);
@@ -315,7 +314,7 @@ namespace Microsoft.AspNet.Identity
 
         private async Task<IdentityResult> ValidatePasswordInternal(TUser user, string password, CancellationToken cancellationToken)
         {
-            var errors = new List<string>();
+            var errors = new List<IdentityError>();
             foreach (var v in PasswordValidators)
             {
                 var result = await v.ValidateAsync(this, user, password, cancellationToken);
@@ -598,7 +597,7 @@ namespace Microsoft.AspNet.Identity
             var hash = await passwordStore.GetPasswordHashAsync(user, cancellationToken);
             if (hash != null)
             {
-                return new IdentityResult(Resources.UserAlreadyHasPassword);
+                return IdentityResult.Failed(ErrorDescriber.UserAlreadyHasPassword());
             }
             var result = await UpdatePasswordInternal(passwordStore, user, password, cancellationToken);
             if (!result.Succeeded)
@@ -634,7 +633,7 @@ namespace Microsoft.AspNet.Identity
                 }
                 return await UpdateAsync(user, cancellationToken);
             }
-            return IdentityResult.Failed(Resources.PasswordMismatch);
+            return IdentityResult.Failed(ErrorDescriber.PasswordMismatch());
         }
 
         /// <summary>
@@ -766,7 +765,7 @@ namespace Microsoft.AspNet.Identity
             // Make sure the token is valid and the stamp matches
             if (!await VerifyUserTokenAsync(user, Options.PasswordResetTokenProvider, "ResetPassword", token, cancellationToken))
             {
-                return IdentityResult.Failed(Resources.InvalidToken);
+                return IdentityResult.Failed(ErrorDescriber.InvalidToken());
             }
             var passwordStore = GetPasswordStore();
             var result = await UpdatePasswordInternal(passwordStore, user, newPassword, cancellationToken);
@@ -877,7 +876,7 @@ namespace Microsoft.AspNet.Identity
             var existingUser = await FindByLoginAsync(login.LoginProvider, login.ProviderKey, cancellationToken);
             if (existingUser != null)
             {
-                return IdentityResult.Failed(Resources.ExternalLoginExists);
+                return IdentityResult.Failed(ErrorDescriber.LoginAlreadyAssociated());
             }
             await loginStore.AddLoginAsync(user, login, cancellationToken);
             return await UpdateAsync(user, cancellationToken);
@@ -1082,7 +1081,7 @@ namespace Microsoft.AspNet.Identity
             var userRoles = await userRoleStore.GetRolesAsync(user, cancellationToken);
             if (userRoles.Contains(role))
             {
-                return new IdentityResult(Resources.UserAlreadyInRole);
+                return IdentityResult.Failed(ErrorDescriber.UserAlreadyInRole(role));
             }
             await userRoleStore.AddToRoleAsync(user, role, cancellationToken);
             return await UpdateAsync(user, cancellationToken);
@@ -1113,7 +1112,7 @@ namespace Microsoft.AspNet.Identity
             {
                 if (userRoles.Contains(role))
                 {
-                    return new IdentityResult(Resources.UserAlreadyInRole);
+                    return IdentityResult.Failed(ErrorDescriber.UserAlreadyInRole(role));
                 }
                 await userRoleStore.AddToRoleAsync(user, role, cancellationToken);
             }
@@ -1138,7 +1137,7 @@ namespace Microsoft.AspNet.Identity
             }
             if (!await userRoleStore.IsInRoleAsync(user, role, cancellationToken))
             {
-                return new IdentityResult(Resources.UserNotInRole);
+                return IdentityResult.Failed(ErrorDescriber.UserNotInRole(role));
             }
             await userRoleStore.RemoveFromRoleAsync(user, role, cancellationToken);
             return await UpdateAsync(user, cancellationToken);
@@ -1168,7 +1167,7 @@ namespace Microsoft.AspNet.Identity
             {
                 if (!await userRoleStore.IsInRoleAsync(user, role, cancellationToken))
                 {
-                    return new IdentityResult(Resources.UserNotInRole);
+                    return IdentityResult.Failed(ErrorDescriber.UserNotInRole(role));
                 }
                 await userRoleStore.RemoveFromRoleAsync(user, role, cancellationToken);
             }
@@ -1313,7 +1312,7 @@ namespace Microsoft.AspNet.Identity
             }
             if (!await VerifyUserTokenAsync(user, Options.EmailConfirmationTokenProvider, "Confirmation", token, cancellationToken))
             {
-                return IdentityResult.Failed(Resources.InvalidToken);
+                return IdentityResult.Failed(ErrorDescriber.InvalidToken());
             }
             await store.SetEmailConfirmedAsync(user, true, cancellationToken);
             return await UpdateAsync(user, cancellationToken);
@@ -1374,7 +1373,7 @@ namespace Microsoft.AspNet.Identity
             // Make sure the token is valid and the stamp matches
             if (!await VerifyUserTokenAsync(user, Options.ChangeEmailTokenProvider, GetChangeEmailPurpose(newEmail), token, cancellationToken))
             {
-                return IdentityResult.Failed(Resources.InvalidToken);
+                return IdentityResult.Failed(ErrorDescriber.InvalidToken());
             }
             var store = GetEmailStore();
             await store.SetEmailAsync(user, newEmail, cancellationToken);
@@ -1453,7 +1452,7 @@ namespace Microsoft.AspNet.Identity
             }
             if (!await VerifyChangePhoneNumberTokenAsync(user, token, phoneNumber, cancellationToken))
             {
-                return IdentityResult.Failed(Resources.InvalidToken);
+                return IdentityResult.Failed(ErrorDescriber.InvalidToken());
             }
             await store.SetPhoneNumberAsync(user, phoneNumber, cancellationToken);
             await store.SetPhoneNumberConfirmedAsync(user, true, cancellationToken);
@@ -1890,7 +1889,7 @@ namespace Microsoft.AspNet.Identity
             }
             if (!await store.GetLockoutEnabledAsync(user, cancellationToken).ConfigureAwait((false)))
             {
-                return IdentityResult.Failed(Resources.LockoutNotEnabled);
+                return IdentityResult.Failed(ErrorDescriber.UserLockoutNotEnabled());
             }
             await store.SetLockoutEndDateAsync(user, lockoutEnd, cancellationToken);
             return await UpdateAsync(user, cancellationToken);

src/Microsoft.AspNet.Identity/UserValidator.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using System.Globalization;
 #if ASPNET50
 using System.Net.Mail;
 #endif
@@ -19,6 +18,13 @@ namespace Microsoft.AspNet.Identity
     /// <typeparam name="TUser"></typeparam>
     public class UserValidator<TUser> : IUserValidator<TUser> where TUser : class
     {
+        public UserValidator(IdentityErrorDescriber errors = null)
+        {
+            Describer = errors ?? new IdentityErrorDescriber();
+        }
+
+        public IdentityErrorDescriber Describer { get; private set; }
+
         /// <summary>
         ///     Validates a user before saving
         /// </summary>
@@ -37,7 +43,7 @@ namespace Microsoft.AspNet.Identity
             {
                 throw new ArgumentNullException("user");
             }
-            var errors = new List<string>();
+            var errors = new List<IdentityError>();
             await ValidateUserName(manager, user, errors);
             if (manager.Options.User.RequireUniqueEmail)
             {
@@ -46,16 +52,16 @@ namespace Microsoft.AspNet.Identity
             return errors.Count > 0 ? IdentityResult.Failed(errors.ToArray()) : IdentityResult.Success;
         }
 
-        private async Task ValidateUserName(UserManager<TUser> manager, TUser user, ICollection<string> errors)
+        private async Task ValidateUserName(UserManager<TUser> manager, TUser user, ICollection<IdentityError> errors)
         {
             var userName = await manager.GetUserNameAsync(user);
             if (string.IsNullOrWhiteSpace(userName))
             {
-                errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.PropertyTooShort, "UserName"));
+                errors.Add(Describer.InvalidUserName(userName));
             }
             else if (manager.Options.User.UserNameValidationRegex != null && !Regex.IsMatch(userName, manager.Options.User.UserNameValidationRegex))
             {
-                errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.InvalidUserName, userName));
+                errors.Add(Describer.InvalidUserName(userName));
             }
             else
             {
@@ -63,18 +69,18 @@ namespace Microsoft.AspNet.Identity
                 if (owner != null && 
                     !string.Equals(await manager.GetUserIdAsync(owner), await manager.GetUserIdAsync(user)))
                 {
-                    errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.DuplicateName, userName));
+                    errors.Add(Describer.DuplicateUserName(userName));
                 }
             }
         }
 
         // make sure email is not empty, valid, and unique
-        private static async Task ValidateEmail(UserManager<TUser> manager, TUser user, List<string> errors)
+        private async Task ValidateEmail(UserManager<TUser> manager, TUser user, List<IdentityError> errors)
         {
             var email = await manager.GetEmailAsync(user);
             if (string.IsNullOrWhiteSpace(email))
             {
-                errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.PropertyTooShort, "Email"));
+                errors.Add(Describer.InvalidEmail(email));
                 return;
             }
 #if ASPNET50
@@ -84,7 +90,7 @@ namespace Microsoft.AspNet.Identity
             }
             catch (FormatException)
             {
-                errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.InvalidEmail, email));
+                errors.Add(Describer.InvalidEmail(email));
                 return;
             }
 #endif
@@ -92,7 +98,7 @@ namespace Microsoft.AspNet.Identity
             if (owner != null && 
                 !string.Equals(await manager.GetUserIdAsync(owner), await manager.GetUserIdAsync(user)))
             {
-                errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.DuplicateEmail, email));
+                errors.Add(Describer.DuplicateEmail(email));
             }
         }
     }

test/Microsoft.AspNet.Identity.InMemory.Test/HttpSignInTest.cs

@@ -50,10 +50,10 @@ namespace Microsoft.AspNet.Identity.InMemory.Test
             var signInManager = app.ApplicationServices.GetRequiredService<SignInManager<ApplicationUser>>();
 
             IdentityResultAssert.IsSuccess(await userManager.CreateAsync(user, password));
-            var result = await signInManager.PasswordSignInAsync(user.UserName, password, isPersistent, false);
+            var result = await signInManager.PasswordSignInAsync(user, password, isPersistent, false);
 
             // Assert
-            Assert.Equal(SignInStatus.Success, result);
+            Assert.True(result.Succeeded);
             context.VerifyAll();
             response.VerifyAll();
             contextAccessor.VerifyAll();

test/Microsoft.AspNet.Identity.Test/IdentityBuilderTest.cs

@@ -226,18 +226,7 @@ namespace Microsoft.AspNet.Identity.Test
 
         private class MyUserManager : UserManager<TestUser>
         {
-            public MyUserManager(IUserStore<TestUser> store,
-            IOptions<IdentityOptions> optionsAccessor,
-            IPasswordHasher<TestUser> passwordHasher,
-            IEnumerable<IUserValidator<TestUser>> userValidators,
-            IEnumerable<IPasswordValidator<TestUser>> passwordValidators,
-            IUserNameNormalizer userNameNormalizer,
-            IEnumerable<IUserTokenProvider<TestUser>> tokenProviders,
-            IEnumerable<IIdentityMessageProvider> msgProviders) :
-                base(store, optionsAccessor, passwordHasher, userValidators, passwordValidators, userNameNormalizer, tokenProviders, msgProviders)
-            {
-
-            }
+            public MyUserManager(IUserStore<TestUser> store) :  base(store) { }
         }
 
         private class MyRoleManager : RoleManager<TestRole>

test/Microsoft.AspNet.Identity.Test/IdentityResultTest.cs

@@ -13,17 +13,15 @@ namespace Microsoft.AspNet.Identity.Test
         {
             var result = new IdentityResult();
             Assert.False(result.Succeeded);
-            Assert.Equal(1, result.Errors.Count());
-            Assert.Equal("An unknown failure has occured.", result.Errors.First());
+            Assert.Equal(0, result.Errors.Count());
         }
 
         [Fact]
-        public void NullErrorListUsesDefaultError()
+        public void NullFailedUsesEmptyErrors()
         {
-            var result = new IdentityResult(null);
+            var result = IdentityResult.Failed();
             Assert.False(result.Succeeded);
-            Assert.Equal(1, result.Errors.Count());
-            Assert.Equal("An unknown failure has occured.", result.Errors.First());
+            Assert.Equal(0, result.Errors.Count());
         }
     }
 }

test/Microsoft.AspNet.Identity.Test/PasswordValidatorTest.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Threading.Tasks;
 using Xunit;
 
@@ -133,13 +134,18 @@ namespace Microsoft.AspNet.Identity.Test
             {
                 errors.Add(upperError);
             }
+            var result = await valid.ValidateAsync(manager, null, input);
             if (errors.Count == 0)
             {
-                IdentityResultAssert.IsSuccess(await valid.ValidateAsync(manager, null, input));
+                IdentityResultAssert.IsSuccess(result);
             }
             else
             {
-                IdentityResultAssert.IsFailure(await valid.ValidateAsync(manager, null, input), string.Join(" ", errors));
+                IdentityResultAssert.IsFailure(result);
+                foreach (var error in errors)
+                {
+                    Assert.True(result.Errors.Any(e => e.Description == error));
+                }
             }
         }
     }

test/Microsoft.AspNet.Identity.Test/RoleValidatorTest.cs

@@ -36,7 +36,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await validator.ValidateAsync(manager, user);
 
             // Assert
-            IdentityResultAssert.IsFailure(result, "Name cannot be null or empty.");
+            IdentityResultAssert.IsFailure(result, IdentityErrorDescriber.Default.InvalidRoleName(input));
         }
     }
 }

test/Microsoft.AspNet.Identity.Test/SignInManagerTest.cs

@@ -1,17 +1,17 @@
 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using Microsoft.AspNet.Http;
-using Microsoft.AspNet.Http.Security;
-using Microsoft.Framework.DependencyInjection;
-using Microsoft.Framework.OptionsModel;
-using Moq;
 using System;
 using System.Collections.Generic;
 using System.Security.Claims;
 using System.Security.Principal;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.AspNet.Http;
+using Microsoft.AspNet.Http.Security;
+using Microsoft.Framework.DependencyInjection;
+using Microsoft.Framework.OptionsModel;
+using Moq;
 using Xunit;
 
 namespace Microsoft.AspNet.Identity.Test
@@ -75,8 +75,6 @@ namespace Microsoft.AspNet.Identity.Test
             var context = new Mock<HttpContext>();
             contextAccessor.Setup(a => a.Value).Returns(context.Object);
             Assert.Throws<ArgumentNullException>("claimsFactory", () => new SignInManager<IdentityUser>(userManager, contextAccessor.Object, null, null));
-            var claimsFactory = new Mock<IClaimsIdentityFactory<IdentityUser>>().Object;
-            Assert.Throws<ArgumentNullException>("optionsAccessor", () => new SignInManager<IdentityUser>(userManager, contextAccessor.Object, claimsFactory, null));
         }
 
         //TODO: Mock fails in K (this works fine in net45)
@@ -132,7 +130,8 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync(user.UserName, "bogus", false, false);
 
             // Assert
-            Assert.Equal(SignInStatus.LockedOut, result);
+            Assert.False(result.Succeeded);
+            Assert.True(result.IsLockedOut);
             manager.VerifyAll();
         }
             
@@ -167,7 +166,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync(user.UserName, "password", isPersistent, false);
 
             // Assert
-            Assert.Equal(SignInStatus.Success, result);
+            Assert.True(result.Succeeded);
             manager.VerifyAll();
             context.VerifyAll();
             response.VerifyAll();
@@ -203,7 +202,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync(user.UserName, "password", false, false);
 
             // Assert
-            Assert.Equal(SignInStatus.Success, result);
+            Assert.True(result.Succeeded);
             manager.VerifyAll();
             context.VerifyAll();
             response.VerifyAll();
@@ -251,7 +250,8 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync(user.UserName, "password", false, false);
 
             // Assert
-            Assert.Equal(SignInStatus.RequiresVerification, result);
+            Assert.False(result.Succeeded);
+            Assert.True(result.RequiresTwoFactor);
             manager.VerifyAll();
             context.VerifyAll();
             response.VerifyAll();
@@ -297,7 +297,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.ExternalLoginSignInAsync(loginProvider, providerKey, isPersistent);
 
             // Assert
-            Assert.Equal(SignInStatus.Success, result);
+            Assert.True(result.Succeeded);
             manager.VerifyAll();
             context.VerifyAll();
             response.VerifyAll();
@@ -382,7 +382,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.TwoFactorSignInAsync(provider, code, isPersistent, rememberClient);
 
             // Assert
-            Assert.Equal(SignInStatus.Success, result);
+            Assert.True(result.Succeeded);
             manager.VerifyAll();
             context.VerifyAll();
             response.VerifyAll();
@@ -466,7 +466,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync(user.UserName, "password", isPersistent, false);
 
             // Assert
-            Assert.Equal(SignInStatus.Success, result);
+            Assert.True(result.Succeeded);
             manager.VerifyAll();
             context.VerifyAll();
             response.VerifyAll();
@@ -530,7 +530,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync(user.UserName, "bogus", false, false);
 
             // Assert
-            Assert.Equal(SignInStatus.Failure, result);
+            Assert.False(result.Succeeded);
             manager.VerifyAll();
             context.VerifyAll();
             contextAccessor.VerifyAll();
@@ -556,7 +556,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync("bogus", "bogus", false, false);
 
             // Assert
-            Assert.Equal(SignInStatus.Failure, result);
+            Assert.False(result.Succeeded);
             manager.VerifyAll();
             context.VerifyAll();
             contextAccessor.VerifyAll();
@@ -592,7 +592,8 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync(user.UserName, "bogus", false, true);
 
             // Assert
-            Assert.Equal(SignInStatus.LockedOut, result);
+            Assert.False(result.Succeeded);
+            Assert.True(result.IsLockedOut);
             manager.VerifyAll();
         }
 
@@ -631,7 +632,9 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync(user, "password", false, false);
 
             // Assert
-            Assert.Equal(confirmed ? SignInStatus.Success : SignInStatus.NotAllowed, result);
+
+            Assert.Equal(confirmed, result.Succeeded);
+            Assert.NotEqual(confirmed, result.IsNotAllowed);
             manager.VerifyAll();
             context.VerifyAll();
             response.VerifyAll();
@@ -670,7 +673,8 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await helper.PasswordSignInAsync(user, "password", false, false);
 
             // Assert
-            Assert.Equal(confirmed ? SignInStatus.Success : SignInStatus.NotAllowed, result);
+            Assert.Equal(confirmed, result.Succeeded);
+            Assert.NotEqual(confirmed, result.IsNotAllowed);
             manager.VerifyAll();
             context.VerifyAll();
             response.VerifyAll();

test/Microsoft.AspNet.Identity.Test/UserManagerTest.cs

@@ -1,16 +1,15 @@
 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using Microsoft.Framework.DependencyInjection;
-using Microsoft.Framework.DependencyInjection.Fallback;
-using Microsoft.Framework.OptionsModel;
-using Moq;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Security.Claims;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.Framework.DependencyInjection;
+using Microsoft.Framework.DependencyInjection.Fallback;
+using Moq;
 using Xunit;
 
 namespace Microsoft.AspNet.Identity.Test
@@ -21,10 +20,7 @@ namespace Microsoft.AspNet.Identity.Test
         {
             public IUserStore<TestUser> StorePublic { get { return Store; } }
 
-            public TestManager(IUserStore<TestUser> store, IOptions<IdentityOptions> optionsAccessor,
-                IPasswordHasher<TestUser> passwordHasher, IEnumerable<IUserValidator<TestUser>> userValidator,
-                IEnumerable<IPasswordValidator<TestUser>> passwordValidator)
-                : base(store, optionsAccessor, passwordHasher, userValidator, passwordValidator, null, null, null) { }
+            public TestManager(IUserStore<TestUser> store) : base(store) { }
         }
 
         [Fact]
@@ -36,8 +32,6 @@ namespace Microsoft.AspNet.Identity.Test
             services.AddIdentity<TestUser, IdentityRole>();
             var manager = services.BuildServiceProvider().GetRequiredService<TestManager>();
             Assert.NotNull(manager.PasswordHasher);
-            Assert.Equal(1, manager.PasswordValidators.Count);
-            Assert.Equal(1, manager.UserValidators.Count);
             Assert.NotNull(manager.StorePublic);
             Assert.NotNull(manager.Options);
         }
@@ -66,7 +60,7 @@ namespace Microsoft.AspNet.Identity.Test
             var store = new Mock<IUserStore<TestUser>>();
             var user = new TestUser { UserName = "Foo" };
             store.Setup(s => s.DeleteAsync(user, CancellationToken.None)).Returns(Task.FromResult(0)).Verifiable();
-            var userManager = MockHelpers.TestUserManager<TestUser>(store.Object);
+            var userManager = MockHelpers.TestUserManager(store.Object);
 
             // Act
             var result = await userManager.DeleteAsync(user);
@@ -100,7 +94,7 @@ namespace Microsoft.AspNet.Identity.Test
             var store = new Mock<IUserStore<TestUser>>();
             var user = new TestUser();
             store.Setup(s => s.SetUserNameAsync(user, It.IsAny<string>(), CancellationToken.None)).Returns(Task.FromResult(0)).Verifiable();
-            var userManager = MockHelpers.TestUserManager<TestUser>(store.Object);
+            var userManager = MockHelpers.TestUserManager(store.Object);
 
             // Act
             var result = await userManager.SetUserNameAsync(user, "foo");
@@ -207,7 +201,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await userManager.AddToRolesAsync(user, roles);
 
             // Assert
-            IdentityResultAssert.IsFailure(result, "User already in role.");
+            IdentityResultAssert.IsFailure(result, IdentityErrorDescriber.Default.UserAlreadyInRole("B"));
             store.VerifyAll();
         }
 
@@ -269,7 +263,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await userManager.RemoveFromRolesAsync(user, roles);
 
             // Assert
-            IdentityResultAssert.IsFailure(result, "User is not in role.");
+            IdentityResultAssert.IsFailure(result, IdentityErrorDescriber.Default.UserNotInRole("B"));
             store.VerifyAll();
         }
 
@@ -284,7 +278,7 @@ namespace Microsoft.AspNet.Identity.Test
                 .Returns(Task.FromResult(0))
                 .Verifiable();
             store.Setup(s => s.UpdateAsync(user, CancellationToken.None)).Returns(Task.FromResult(0)).Verifiable();
-            var userManager = MockHelpers.TestUserManager<TestUser>(store.Object);
+            var userManager = MockHelpers.TestUserManager(store.Object);
 
             // Act
             var result = await userManager.AddClaimsAsync(user, claims);
@@ -305,7 +299,7 @@ namespace Microsoft.AspNet.Identity.Test
                 .Returns(Task.FromResult(0))
                 .Verifiable();
             store.Setup(s => s.UpdateAsync(user, CancellationToken.None)).Returns(Task.FromResult(0)).Verifiable();
-            var userManager = MockHelpers.TestUserManager<TestUser>(store.Object);
+            var userManager = MockHelpers.TestUserManager(store.Object);
 
             // Act
             var result = await userManager.AddClaimAsync(user, claim);
@@ -326,7 +320,7 @@ namespace Microsoft.AspNet.Identity.Test
             store.Setup(s => s.ReplaceClaimAsync(user, It.IsAny<Claim>(), It.IsAny<Claim>(), CancellationToken.None))
                 .Returns(Task.FromResult(0))
                 .Verifiable();
-            var userManager = MockHelpers.TestUserManager<TestUser>(store.Object);
+            var userManager = MockHelpers.TestUserManager(store.Object);
 
             // Act
             var result = await userManager.ReplaceClaimAsync(user, claim, newClaim);
@@ -533,17 +527,11 @@ namespace Microsoft.AspNet.Identity.Test
         public async Task ManagerPublicNullChecks()
         {
             var store = new NotImplementedStore();
-            var optionsAccessor = new OptionsManager<IdentityOptions>(null);
-            var passwordHasher = new PasswordHasher<TestUser>(new PasswordHasherOptionsAccessor());
 
             Assert.Throws<ArgumentNullException>("store",
-                () => new UserManager<TestUser>(null, null, null, null, null, null, null, null));
-            Assert.Throws<ArgumentNullException>("optionsAccessor",
-                () => new UserManager<TestUser>(store, null, null, null, null, null, null, null));
-            Assert.Throws<ArgumentNullException>("passwordHasher",
-                () => new UserManager<TestUser>(store, optionsAccessor, null, null, null, null, null, null));
+                () => new UserManager<TestUser>(null));
 
-            var manager = new UserManager<TestUser>(store, optionsAccessor, passwordHasher, null, null, null, null, null);
+            var manager = new UserManager<TestUser>(store);
 
             Assert.Throws<ArgumentNullException>("value", () => manager.PasswordHasher = null);
             Assert.Throws<ArgumentNullException>("value", () => manager.Options = null);
@@ -714,7 +702,7 @@ namespace Microsoft.AspNet.Identity.Test
 
         private class BadPasswordValidator<TUser> : IPasswordValidator<TUser> where TUser : class
         {
-            public const string ErrorMessage = "I'm Bad.";
+            public static readonly IdentityError ErrorMessage = new IdentityError { Description = "I'm Bad." };
 
             public Task<IdentityResult> ValidateAsync(UserManager<TUser> manager, TUser user, string password, CancellationToken cancellationToken = default(CancellationToken))
             {
@@ -1239,5 +1227,51 @@ namespace Microsoft.AspNet.Identity.Test
                 throw new NotImplementedException();
             }
         }
+
+        [Fact]
+        public async Task CanCustomizeUserValidatorErrors()
+        {
+            var services = new ServiceCollection();
+            var store = new Mock<IUserEmailStore<TestUser>>();
+            var describer = new TestErrorDescriber();
+            services.AddInstance<IdentityErrorDescriber>(describer)
+                .AddInstance<IUserStore<TestUser>>(store.Object)
+                .AddIdentity<TestUser, IdentityRole>();
+
+            var manager = services.BuildServiceProvider().GetRequiredService<UserManager<TestUser>>();
+
+            manager.Options.User.RequireUniqueEmail = true;
+            var user = new TestUser() { UserName = "dupeEmail", Email = "dupe@email.com" };
+            var user2 = new TestUser() { UserName = "dupeEmail2", Email = "dupe@email.com" };
+            store.Setup(s => s.FindByEmailAsync(user.Email, CancellationToken.None))
+                .Returns(Task.FromResult(user2))
+                .Verifiable();
+            store.Setup(s => s.GetUserIdAsync(user2, CancellationToken.None))
+                .Returns(Task.FromResult(user2.Id))
+                .Verifiable();
+            store.Setup(s => s.GetUserNameAsync(user, CancellationToken.None))
+                .Returns(Task.FromResult(user.UserName))
+                .Verifiable();
+            store.Setup(s => s.GetEmailAsync(user, CancellationToken.None))
+                .Returns(Task.FromResult(user.Email))
+                .Verifiable();
+
+            Assert.Same(describer, manager.ErrorDescriber);
+            IdentityResultAssert.IsFailure(await manager.CreateAsync(user), describer.DuplicateEmail(user.Email));
+
+            store.VerifyAll();
+        }
+
+        public class TestErrorDescriber : IdentityErrorDescriber
+        {
+            public static string Code = "Error";
+            public static string FormatError = "FormatError {0}";
+
+            public override IdentityError DuplicateEmail(string email)
+            {
+                return new IdentityError { Code = Code, Description = string.Format(FormatError, email) };
+            }
+        }
+
     }
 }

test/Microsoft.AspNet.Identity.Test/UserValidatorTest.cs

@@ -36,7 +36,7 @@ namespace Microsoft.AspNet.Identity.Test
             var result = await validator.ValidateAsync(manager, user);
 
             // Assert
-            IdentityResultAssert.IsFailure(result, "UserName cannot be null or empty.");
+            IdentityResultAssert.IsFailure(result, IdentityErrorDescriber.Default.InvalidUserName(input));
         }
 
         [Theory]

test/Shared/IdentityResultAssert.cs

@@ -24,7 +24,16 @@ namespace Microsoft.AspNet.Identity.Test
         {
             Assert.NotNull(result);
             Assert.False(result.Succeeded);
-            Assert.Equal(error, result.Errors.First());
+            Assert.Equal(error, result.Errors.First().Description);
         }
+
+        public static void IsFailure(IdentityResult result, IdentityError error)
+        {
+            Assert.NotNull(result);
+            Assert.False(result.Succeeded);
+            Assert.Equal(error.Description, result.Errors.First().Description);
+            Assert.Equal(error.Code, result.Errors.First().Code);
+        }
+
     }
 }

test/Shared/MockHelpers.cs

@@ -14,20 +14,10 @@ namespace Microsoft.AspNet.Identity.Test
         public static Mock<UserManager<TUser>> MockUserManager<TUser>() where TUser : class
         {
             var store = new Mock<IUserStore<TUser>>();
-            var options = new OptionsManager<IdentityOptions>(null);
-            var userValidators = new List<IUserValidator<TUser>>();
-            userValidators.Add(new UserValidator<TUser>());
-            var pwdValidators = new List<IPasswordValidator<TUser>>();
-            pwdValidators.Add(new PasswordValidator<TUser>());
-            return new Mock<UserManager<TUser>>(
-                store.Object,
-                options,
-                new PasswordHasher<TUser>(new PasswordHasherOptionsAccessor()),
-                userValidators,
-                pwdValidators,
-                new UpperInvariantUserNameNormalizer(),
-                new List<IUserTokenProvider<TUser>>(),
-                new List<IIdentityMessageProvider>());
+            var mgr = new Mock<UserManager<TUser>>(store.Object, null, null, null, null, null, null, null, null);
+            mgr.Object.UserValidators.Add(new UserValidator<TUser>());
+            mgr.Object.PasswordValidators.Add(new PasswordValidator<TUser>());
+            return mgr;
         }
 
         public static Mock<RoleManager<TRole>> MockRoleManager<TRole>() where TRole : class
@@ -35,7 +25,7 @@ namespace Microsoft.AspNet.Identity.Test
             var store = new Mock<IRoleStore<TRole>>();
             var roles = new List<IRoleValidator<TRole>>();
             roles.Add(new RoleValidator<TRole>());
-            return new Mock<RoleManager<TRole>>(store.Object, roles);
+            return new Mock<RoleManager<TRole>>(store.Object, roles, null);
         }
 
         public static UserManager<TUser> TestUserManager<TUser>() where TUser : class
@@ -45,10 +35,8 @@ namespace Microsoft.AspNet.Identity.Test
 
         public static UserManager<TUser> TestUserManager<TUser>(IUserStore<TUser> store) where TUser : class
         {
-            var options = new OptionsManager<IdentityOptions>(null);
-            var validator = new Mock<UserValidator<TUser>>();
-            var userManager = new UserManager<TUser>(store, options, new PasswordHasher<TUser>(new PasswordHasherOptionsAccessor()), 
-                null, null, new UpperInvariantUserNameNormalizer(), null, null);
+            var validator = new Mock<IUserValidator<TUser>>();
+            var userManager = new UserManager<TUser>(store);
             userManager.UserValidators.Add(validator.Object);
             userManager.PasswordValidators.Add(new PasswordValidator<TUser>());
             validator.Setup(v => v.ValidateAsync(userManager, It.IsAny<TUser>(), CancellationToken.None))

test/Shared/TestUser.cs

@@ -14,5 +14,6 @@ namespace Microsoft.AspNet.Identity.Test
 
         public string Id { get; private set; }
         public string UserName { get; set; }
+        public string Email { get; set; }
     }
 }

test/Shared/UserManagerTestBase.cs

@@ -182,7 +182,7 @@ namespace Microsoft.AspNet.Identity.Test
             var manager = CreateManager();
             var user = CreateTestUser();
             manager.Options.User.RequireUniqueEmail = true;
-            IdentityResultAssert.IsFailure(await manager.CreateAsync(user), "Email cannot be null or empty.");
+            IdentityResultAssert.IsFailure(await manager.CreateAsync(user), IdentityErrorDescriber.Default.InvalidEmail(email));
         }
 
 #if ASPNET50
@@ -194,7 +194,7 @@ namespace Microsoft.AspNet.Identity.Test
             var manager = CreateManager();
             var user = new TUser() { UserName = "UpdateBlocked", Email = email };
             manager.Options.User.RequireUniqueEmail = true;
-            IdentityResultAssert.IsFailure(await manager.CreateAsync(user), "Email '" + email + "' is invalid.");
+            IdentityResultAssert.IsFailure(await manager.CreateAsync(user), IdentityErrorDescriber.Default.InvalidEmail(email));
         }
 #endif
 
@@ -414,7 +414,7 @@ namespace Microsoft.AspNet.Identity.Test
             var user = CreateTestUser();
             var user2 = new TUser() { UserName = user.UserName };
             IdentityResultAssert.IsSuccess(await manager.CreateAsync(user));
-            IdentityResultAssert.IsFailure(await manager.CreateAsync(user2), "Name "+user.UserName+" is already taken.");
+            IdentityResultAssert.IsFailure(await manager.CreateAsync(user2), IdentityErrorDescriber.Default.DuplicateUserName(user.UserName));
         }
 
         [Fact]
@@ -440,7 +440,7 @@ namespace Microsoft.AspNet.Identity.Test
             user.Email = email;
             user2.Email = email;
             IdentityResultAssert.IsSuccess(await manager.CreateAsync(user));
-            IdentityResultAssert.IsFailure(await manager.CreateAsync(user2), "Email '"+email+"' is already taken.");
+            IdentityResultAssert.IsFailure(await manager.CreateAsync(user2), IdentityErrorDescriber.Default.DuplicateEmail(user.Email));
         }
 
         [Fact]
@@ -465,7 +465,7 @@ namespace Microsoft.AspNet.Identity.Test
             IdentityResultAssert.IsSuccess(await manager.CreateAsync(user));
             IdentityResultAssert.IsSuccess(await manager.AddLoginAsync(user, login));
             var result = await manager.AddLoginAsync(user, login);
-            IdentityResultAssert.IsFailure(result, "A user with that external login already exists.");
+            IdentityResultAssert.IsFailure(result, IdentityErrorDescriber.Default.LoginAlreadyAssociated());
         }
 
         // Email tests
@@ -842,7 +842,7 @@ namespace Microsoft.AspNet.Identity.Test
         private class AlwaysBadValidator : IUserValidator<TUser>, IRoleValidator<TRole>,
             IPasswordValidator<TUser>
         {
-            public const string ErrorMessage = "I'm Bad.";
+            public static readonly IdentityError ErrorMessage = new IdentityError { Description = "I'm Bad." };
 
             public Task<IdentityResult> ValidateAsync(UserManager<TUser> manager, TUser user, string password, CancellationToken cancellationToken = default(CancellationToken))
             {
@@ -1142,7 +1142,7 @@ namespace Microsoft.AspNet.Identity.Test
             IdentityResultAssert.IsSuccess(await userMgr.CreateAsync(user));
             IdentityResultAssert.IsSuccess(await roleMgr.CreateAsync(role));
             var result = await userMgr.RemoveFromRoleAsync(user, role.Name);
-            IdentityResultAssert.IsFailure(result, "User is not in role.");
+            IdentityResultAssert.IsFailure(result, IdentityErrorDescriber.Default.UserNotInRole(role.Name));
         }
 
         [Fact]
@@ -1157,7 +1157,7 @@ namespace Microsoft.AspNet.Identity.Test
             IdentityResultAssert.IsSuccess(await roleMgr.CreateAsync(role));
             IdentityResultAssert.IsSuccess(await userMgr.AddToRoleAsync(user, role.Name));
             Assert.True(await userMgr.IsInRoleAsync(user, role.Name));
-            IdentityResultAssert.IsFailure(await userMgr.AddToRoleAsync(user, role.Name), "User already in role.");
+            IdentityResultAssert.IsFailure(await userMgr.AddToRoleAsync(user, role.Name), IdentityErrorDescriber.Default.UserAlreadyInRole(role.Name));
         }
 
         [Fact]