Add GetAuthenticateInfo method

src/Microsoft.AspNetCore.Http.Abstractions/Authentication/AuthenticateInfo.cs

@@ -0,0 +1,24 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Security.Claims;
+
+namespace Microsoft.AspNetCore.Http.Authentication
+{
+    /// <summary>
+    /// Used to store the results of an Authenticate call.
+    /// </summary>
+    public class AuthenticateInfo
+    {
+        /// <summary>
+        /// The <see cref="ClaimsPrincipal"/>.
+        /// </summary>
+        public ClaimsPrincipal Principal { get; set; }
+
+        /// <summary>
+        /// The <see cref="AuthenticationProperties"/>.
+        /// </summary>
+        public AuthenticationProperties Properties { get; set; }
+    }
+}

src/Microsoft.AspNetCore.Http.Abstractions/Authentication/AuthenticationManager.cs

@@ -20,18 +20,14 @@ namespace Microsoft.AspNetCore.Http.Authentication
 
         public abstract IEnumerable<AuthenticationDescription> GetAuthenticationSchemes();
 
+        public abstract Task<AuthenticateInfo> GetAuthenticateInfoAsync(string authenticationScheme);
+
+        // Will remove once callees have been updated
         public abstract Task AuthenticateAsync(AuthenticateContext context);
 
         public virtual async Task<ClaimsPrincipal> AuthenticateAsync(string authenticationScheme)
         {
-            if (authenticationScheme == null)
-            {
-                throw new ArgumentNullException(nameof(authenticationScheme));
-            }
-
-            var context = new AuthenticateContext(authenticationScheme);
-            await AuthenticateAsync(context);
-            return context.Principal;
+            return (await GetAuthenticateInfoAsync(authenticationScheme))?.Principal;
         }
 
         public virtual Task ChallengeAsync()

src/Microsoft.AspNetCore.Http/Authentication/DefaultAuthenticationManager.cs

@@ -50,6 +50,7 @@ namespace Microsoft.AspNetCore.Http.Authentication.Internal
             return describeContext.Results.Select(description => new AuthenticationDescription(description));
         }
 
+        // Remove once callers have been switched to GetAuthenticateInfoAsync
         public override async Task AuthenticateAsync(AuthenticateContext context)
         {
             if (context == null)
@@ -69,6 +70,32 @@ namespace Microsoft.AspNetCore.Http.Authentication.Internal
             }
         }
 
+        public override async Task<AuthenticateInfo> GetAuthenticateInfoAsync(string authenticationScheme)
+        {
+            if (authenticationScheme == null)
+            {
+                throw new ArgumentNullException(nameof(authenticationScheme));
+            }
+
+            var handler = HttpAuthenticationFeature.Handler;
+            var context = new AuthenticateContext(authenticationScheme);
+            if (handler != null)
+            {
+                await handler.AuthenticateAsync(context);
+            }
+
+            if (!context.Accepted)
+            {
+                throw new InvalidOperationException($"No authentication handler is configured to authenticate for the scheme: {context.AuthenticationScheme}");
+            }
+
+            return new AuthenticateInfo
+            {
+                Principal = context.Principal,
+                Properties = new AuthenticationProperties(context.Properties)
+            };
+        }
+
         public override async Task ChallengeAsync(string authenticationScheme, AuthenticationProperties properties, ChallengeBehavior behavior)
         {
             if (string.IsNullOrEmpty(authenticationScheme))