Make AuthenticateAsync return non-null result (#22708)

* Make AuthenticateAsync return non-null result

* NoResult

src/Http/Authentication.Abstractions/ref/Microsoft.AspNetCore.Authentication.Abstractions.netcoreapp.cs

@@ -22,8 +22,8 @@ namespace Microsoft.AspNetCore.Authentication
     }
     public static partial class AuthenticationHttpContextExtensions
     {
-        public static System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticateResult?> AuthenticateAsync(this Microsoft.AspNetCore.Http.HttpContext context) { throw null; }
+        public static System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticateResult> AuthenticateAsync(this Microsoft.AspNetCore.Http.HttpContext context) { throw null; }
-        public static System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticateResult?> AuthenticateAsync(this Microsoft.AspNetCore.Http.HttpContext context, string? scheme) { throw null; }
+        public static System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticateResult> AuthenticateAsync(this Microsoft.AspNetCore.Http.HttpContext context, string? scheme) { throw null; }
         public static System.Threading.Tasks.Task ChallengeAsync(this Microsoft.AspNetCore.Http.HttpContext context) { throw null; }
         public static System.Threading.Tasks.Task ChallengeAsync(this Microsoft.AspNetCore.Http.HttpContext context, Microsoft.AspNetCore.Authentication.AuthenticationProperties? properties) { throw null; }
         public static System.Threading.Tasks.Task ChallengeAsync(this Microsoft.AspNetCore.Http.HttpContext context, string scheme) { throw null; }
@@ -157,7 +157,7 @@ namespace Microsoft.AspNetCore.Authentication
     }
     public partial interface IAuthenticationService
     {
-        System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticateResult?> AuthenticateAsync(Microsoft.AspNetCore.Http.HttpContext context, string? scheme);
+        System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticateResult> AuthenticateAsync(Microsoft.AspNetCore.Http.HttpContext context, string? scheme);
         System.Threading.Tasks.Task ChallengeAsync(Microsoft.AspNetCore.Http.HttpContext context, string? scheme, Microsoft.AspNetCore.Authentication.AuthenticationProperties? properties);
         System.Threading.Tasks.Task ForbidAsync(Microsoft.AspNetCore.Http.HttpContext context, string? scheme, Microsoft.AspNetCore.Authentication.AuthenticationProperties? properties);
         System.Threading.Tasks.Task SignInAsync(Microsoft.AspNetCore.Http.HttpContext context, string? scheme, System.Security.Claims.ClaimsPrincipal principal, Microsoft.AspNetCore.Authentication.AuthenticationProperties? properties);

src/Http/Authentication.Abstractions/src/AuthenticationHttpContextExtensions.cs

@@ -18,7 +18,7 @@ namespace Microsoft.AspNetCore.Authentication
         /// </summary>
         /// <param name="context">The <see cref="HttpContext"/> context.</param>
         /// <returns>The <see cref="AuthenticateResult"/>.</returns>
-        public static Task<AuthenticateResult?> AuthenticateAsync(this HttpContext context) =>
+        public static Task<AuthenticateResult> AuthenticateAsync(this HttpContext context) =>
             context.AuthenticateAsync(scheme: null);
 
         /// <summary>
@@ -27,7 +27,7 @@ namespace Microsoft.AspNetCore.Authentication
         /// <param name="context">The <see cref="HttpContext"/> context.</param>
         /// <param name="scheme">The name of the authentication scheme.</param>
         /// <returns>The <see cref="AuthenticateResult"/>.</returns>
-        public static Task<AuthenticateResult?> AuthenticateAsync(this HttpContext context, string? scheme) =>
+        public static Task<AuthenticateResult> AuthenticateAsync(this HttpContext context, string? scheme) =>
             context.RequestServices.GetRequiredService<IAuthenticationService>().AuthenticateAsync(context, scheme);
 
         /// <summary>

src/Http/Authentication.Abstractions/src/IAuthenticationService.cs

@@ -18,7 +18,7 @@ namespace Microsoft.AspNetCore.Authentication
         /// <param name="context">The <see cref="HttpContext"/>.</param>
         /// <param name="scheme">The name of the authentication scheme.</param>
         /// <returns>The result.</returns>
-        Task<AuthenticateResult?> AuthenticateAsync(HttpContext context, string? scheme);
+        Task<AuthenticateResult> AuthenticateAsync(HttpContext context, string? scheme);
 
         /// <summary>
         /// Challenge the specified authentication scheme.

src/Http/Authentication.Core/ref/Microsoft.AspNetCore.Authentication.Core.netcoreapp.cs

@@ -40,7 +40,7 @@ namespace Microsoft.AspNetCore.Authentication
         public Microsoft.AspNetCore.Authentication.IAuthenticationSchemeProvider Schemes { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public Microsoft.AspNetCore.Authentication.IClaimsTransformation Transform { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         [System.Diagnostics.DebuggerStepThroughAttribute]
-        public virtual System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticateResult?> AuthenticateAsync(Microsoft.AspNetCore.Http.HttpContext context, string? scheme) { throw null; }
+        public virtual System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticateResult> AuthenticateAsync(Microsoft.AspNetCore.Http.HttpContext context, string? scheme) { throw null; }
         [System.Diagnostics.DebuggerStepThroughAttribute]
         public virtual System.Threading.Tasks.Task ChallengeAsync(Microsoft.AspNetCore.Http.HttpContext context, string? scheme, Microsoft.AspNetCore.Authentication.AuthenticationProperties? properties) { throw null; }
         [System.Diagnostics.DebuggerStepThroughAttribute]

src/Http/Authentication.Core/src/AuthenticationService.cs

@@ -59,7 +59,7 @@ namespace Microsoft.AspNetCore.Authentication
         /// <param name="context">The <see cref="HttpContext"/>.</param>
         /// <param name="scheme">The name of the authentication scheme.</param>
         /// <returns>The result.</returns>
-        public virtual async Task<AuthenticateResult?> AuthenticateAsync(HttpContext context, string? scheme)
+        public virtual async Task<AuthenticateResult> AuthenticateAsync(HttpContext context, string? scheme)
         {
             if (scheme == null)
             {
@@ -77,8 +77,10 @@ namespace Microsoft.AspNetCore.Authentication
                 throw await CreateMissingHandlerException(scheme);
             }
 
-            var result = await handler.AuthenticateAsync();
+            // Handlers should not return null, but we'll be tolerant of null values for legacy reasons.
-            if (result != null && result.Succeeded)
+            var result = (await handler.AuthenticateAsync()) ?? AuthenticateResult.NoResult();
+
+            if (result.Succeeded)
             {
                 var principal = result.Principal!;
                 var doTransform = true;