Fix for #415 (#428)

domain_hint ingored when login_hint is set.
Break up code so that domain_hint and login_hint are treated
independently.

Co-authored-by: Thibault Durand <thibault.durand@liu.se>

src/Microsoft.Identity.Web/WebAppExtensions/WebAppAuthenticationBuilderExtensions.cs

@@ -136,12 +136,19 @@ public static AuthenticationBuilder AddMicrosoftWebApp(
                     if (!string.IsNullOrWhiteSpace(login))
                     {
                         context.ProtocolMessage.LoginHint = login;
-                        context.ProtocolMessage.DomainHint = context.Properties.GetParameter<string>(
-                            OpenIdConnectParameterNames.DomainHint);
 
-                        // delete the login_hint and domainHint from the Properties when we are done otherwise
+                        // delete the login_hint from the Properties when we are done otherwise
                         // it will take up extra space in the cookie.
                         context.Properties.Parameters.Remove(OpenIdConnectParameterNames.LoginHint);
+                    }
+
+                    var domainHint = context.Properties.GetParameter<string>(OpenIdConnectParameterNames.DomainHint);
+                    if (!string.IsNullOrWhiteSpace(domainHint))
+                    {
+                        context.ProtocolMessage.DomainHint = domainHint;
+
+                        // delete the domain_hint from the Properties when we are done otherwise
+                        // it will take up extra space in the cookie.
                         context.Properties.Parameters.Remove(OpenIdConnectParameterNames.DomainHint);
                     }