WinHttpHandler: Check available credentials when choosing authentication scheme

src/System.Net.Http.WinHttpHandler/src/System/Net/Http/WinHttpAuthHelper.cs

@@ -102,7 +102,7 @@ public void CheckResponseForAuthentication(
                     // But we can validate with assert.
                     Debug.Assert(authTarget == Interop.WinHttp.WINHTTP_AUTH_TARGET_SERVER);
 
-                    serverAuthScheme = ChooseAuthScheme(supportedSchemes);
+                    serverAuthScheme = ChooseAuthScheme(supportedSchemes, state.RequestMessage.RequestUri, state.ServerCredentials);
                     if (serverAuthScheme != 0)
                     {
                         if (SetWinHttpCredential(
@@ -155,7 +155,7 @@ public void CheckResponseForAuthentication(
                     // But we can validate with assert.
                     Debug.Assert(authTarget == Interop.WinHttp.WINHTTP_AUTH_TARGET_PROXY);
 
-                    proxyAuthScheme = ChooseAuthScheme(supportedSchemes);
+                    proxyAuthScheme = ChooseAuthScheme(supportedSchemes, state.Proxy.GetProxy(state.RequestMessage.RequestUri), proxyCreds);
                     state.RetryRequest = true;
                     break;
 
@@ -371,11 +371,16 @@ private bool SetWinHttpCredential(
             return true;
         }
 
-        private static uint ChooseAuthScheme(uint supportedSchemes)
+        private static uint ChooseAuthScheme(uint supportedSchemes, Uri uri, ICredentials credentials)
         {
+            if (credentials == null)
+            {
+                return 0;
+            }
+
             foreach (uint authScheme in s_authSchemePriorityOrder)
             {
-                if ((supportedSchemes & authScheme) != 0)
+                if ((supportedSchemes & authScheme) != 0 && credentials.GetCredential(uri, s_authSchemeStringMapping[authScheme]) != null)
                 {
                     return authScheme;
                 }

src/System.Net.Http/tests/FunctionalTests/HttpClientHandlerTest.Authentication.cs

@@ -19,7 +19,7 @@ public abstract class HttpClientHandler_Authentication_Test : HttpClientTestBase
 
         private static readonly NetworkCredential s_credentials = new NetworkCredential(Username, Password, Domain);
 
-        private static readonly Func<HttpClientHandler, Uri, HttpStatusCode, NetworkCredential, Task> s_createAndValidateRequest = async (handler, url, expectedStatusCode, credentials) =>
+        private static readonly Func<HttpClientHandler, Uri, HttpStatusCode, ICredentials, Task> s_createAndValidateRequest = async (handler, url, expectedStatusCode, credentials) =>
         {
             handler.Credentials = credentials;
 
@@ -90,6 +90,31 @@ await LoopbackServer.CreateServerAsync(async (server, url) =>
             }, options);
         }
 
+        [Theory]
+        [InlineData("WWW-Authenticate: Basic realm=\"hello\"\r\nWWW-Authenticate: Negotiate\r\nx-identifier: Test\r\n", "Basic")]
+        [InlineData("WWW-Authenticate: Basic realm=\"hello\"\r\nWWW-Authenticate: Digest realm=\"hello\", nonce=\"hello\", algorithm=MD5\r\nWWW-Authenticate: Negotiate\r\nx-identifier: Test\r\n", "Digest")]
+        public async Task HttpClientHandler_MultipleAuthenticateHeaders_PicksSupported(string authenticateHeader, string supportedAuth)
+        {
+            if (IsCurlHandler && authenticateHeader.Contains("Digest"))
+            {
+                // TODO: #28065: Fix failing authentication test cases on different httpclienthandlers.
+                return;
+            }
+
+            var options = new LoopbackServer.Options { Domain = Domain, Username = Username, Password = Password };
+            await LoopbackServer.CreateServerAsync(async (server, url) =>
+            {
+                HttpClientHandler handler = CreateHttpClientHandler();
+
+                var credentials = new CredentialCache();
+                credentials.Add(url, supportedAuth, new NetworkCredential(Username, Password, Domain));
+                handler.UseDefaultCredentials = false;
+
+                Task serverTask = server.AcceptConnectionPerformAuthenticationAndCloseAsync(authenticateHeader);
+                await TestHelper.WhenAllCompletedOrAnyFailed(s_createAndValidateRequest(handler, url, HttpStatusCode.OK, credentials), serverTask);
+            }, options);
+        }
+
         [Theory]
         [InlineData("WWW-Authenticate: Basic realm=\"hello\"\r\n")]
         [InlineData("WWW-Authenticate: Digest realm=\"hello\", nonce=\"testnonce\"\r\n")]