Restore AuthenticateAsync for now

Author: HaoK

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

@@ -22,6 +22,9 @@ public abstract class AuthenticationManager
 
         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)
         {
             return (await GetAuthenticateInfoAsync(authenticationScheme))?.Principal;

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

@@ -50,6 +50,26 @@ public override IEnumerable<AuthenticationDescription> GetAuthenticationSchemes(
             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)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            var handler = HttpAuthenticationFeature.Handler;
+            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}");
+            }
+        }
+
         public override async Task<AuthenticateInfo> GetAuthenticateInfoAsync(string authenticationScheme)
         {
             if (authenticationScheme == null)