Handle failed authentication

Morphic.Service/HttpService.cs

@@ -106,7 +106,11 @@ public HttpService(Uri endpoint, IHttpServiceCredentialsProvider credentialsProv
             }
             catch (BadRequestException e)
             {
-                throw e;
+                // OBSERVATION: in our testing, this occurred in scenarios like logging in with an invalid username/password combination (such as after changing a password online); throwing an unhandled exception would not be an appropriate response
+                System.Diagnostics.Debug.Assert(false, "BadRequest; exception: " + e.Message);
+                logger.LogError(e, "Request failed");
+                return null;
+//                throw e;
             }
             catch (Exception e)
             {

Morphic.Service/MorphicSession.cs

@@ -67,7 +67,13 @@ public override async Task OpenAsync()
             // NOTE: ideally we would not re-authenticate and re-load the MorphicBars before loading the current bar (i.e. ideally we would cache this data, like we do on macOS)
             if (this.CurrentCredentials is UsernameCredentials credentials)
             {
-                await this.Authenticate(credentials, false);
+                var authenticateSuccess = await this.Authenticate(credentials, false);
+                if (authenticateSuccess == false)
+                {
+                    // user could not be logged in; reverse user to null
+                    // OBSERVATION: this is not the cleanest way to handle a failed authentication attempt; in the future, we should prompt the user to let them know that authentication failed (and why...either a busy server or a bad login credential, etc.)--and they should know they're not logged in AND they should have the opportunity to sign in (assuming the server is not busy)
+                    this.User = null;
+                }
             }
             //
             // cache our user id (so that we don't re-call "user changed" if our user doesn't actually change here)