Reset negotiateAuth if SNI doesn't work

Author: twsouthwick

src/Microsoft.Data.SqlClient/src/Microsoft/Data/SqlClient/SSPI/NegotiateSspiContextProvider.cs

@@ -16,6 +16,12 @@ protected override bool GenerateSspiClientContext(ReadOnlySpan<byte> incomingBlo
         {
             NegotiateAuthenticationStatusCode statusCode = NegotiateAuthenticationStatusCode.UnknownCredentials;
 
+            // If we've already successfully performed the negotiate we only want to do it for the original target
+            if (_negotiateAuth is { TargetName: { } name } && name != authParams.Resource)
+            {
+                return false;
+            }
+
             _negotiateAuth ??= new(new NegotiateAuthenticationClientOptions { Package = "Negotiate", TargetName = authParams.Resource });
             var sendBuff = _negotiateAuth.GetOutgoingBlob(incomingBlob, out statusCode)!;
 
@@ -29,6 +35,8 @@ protected override bool GenerateSspiClientContext(ReadOnlySpan<byte> incomingBlo
                 return true;
             }
 
+            // Reset _negotiateAuth to be generated again for next SPN.
+            _negotiateAuth = null;
             return false;
         }
     }