Fix SignInResult with default scheme (#27531)

Description
Fixes #27494

A community PR introduced new overloads to ControllerBase for SignIn. The new overload throws due to an existing check which blocks when the scheme is null. The fix is to remove this unnecessary check. Note SignOutResult already had test coverage for this usage and is unaffected

Customer Impact
The bug was reported by a customer trying to use the new overload. The fix enables the method to be used.

Regression?
No

Risk
Low as this is a new API, and the api was unuseable in its current form.

Author: HaoK

src/Mvc/Mvc.Core/src/SignInResult.cs

@@ -85,14 +85,6 @@ public override async Task ExecuteResultAsync(ActionContext context)
                 throw new ArgumentNullException(nameof(context));
             }
 
-            if (AuthenticationScheme == null)
-            {
-                throw new InvalidOperationException(
-                    Resources.FormatPropertyOfTypeCannotBeNull(
-                        /* property: */ nameof(AuthenticationScheme),
-                        /* type: */ nameof(SignInResult)));
-            }
-
             var loggerFactory = context.HttpContext.RequestServices.GetRequiredService<ILoggerFactory>();
             var logger = loggerFactory.CreateLogger<SignInResult>();
 

src/Mvc/Mvc.Core/test/SignInResultTest.cs

@@ -45,6 +45,33 @@ public async Task ExecuteResultAsync_InvokesSignInAsyncOnAuthenticationManager()
             auth.Verify();
         }
 
+        [Fact]
+        public async Task ExecuteResultAsync_InvokesSignInAsyncOnAuthenticationManagerWithDefaultScheme()
+        {
+            // Arrange
+            var principal = new ClaimsPrincipal();
+            var httpContext = new Mock<HttpContext>();
+            var auth = new Mock<IAuthenticationService>();
+            auth
+                .Setup(c => c.SignInAsync(httpContext.Object, null, principal, null))
+                .Returns(Task.CompletedTask)
+                .Verifiable();
+            httpContext.Setup(c => c.RequestServices).Returns(CreateServices(auth.Object));
+            var result = new SignInResult(principal);
+            var routeData = new RouteData();
+
+            var actionContext = new ActionContext(
+                httpContext.Object,
+                routeData,
+                new ActionDescriptor());
+
+            // Act
+            await result.ExecuteResultAsync(actionContext);
+
+            // Assert
+            auth.Verify();
+        }
+
         [Fact]
         public async Task ExecuteResultAsync_InvokesSignInAsyncOnConfiguredScheme()
         {
@@ -81,4 +108,4 @@ private static IServiceProvider CreateServices(IAuthenticationService auth)
                 .BuildServiceProvider();
         }
     }
-}
+}