Updated GMailOAuth2.md

GMailOAuth2.md

@@ -78,11 +78,13 @@ var codeFlow = new GoogleAuthorizationCodeFlow (new GoogleAuthorizationCodeFlow.
 	ClientSecrets = clientSecrets
 });
 
+// Note: For a web app, you'll want to use AuthorizationCodeWebApp instead.
 var codeReceiver = new LocalServerCodeReceiver ();
 var authCode = new AuthorizationCodeInstalledApp (codeFlow, codeReceiver);
+
 var credential = await authCode.AuthorizeAsync (GMailAccount, CancellationToken.None);
 
-if (authCode.ShouldRequestAuthorizationCode (credential.Token))
+if (credential.Token.IsExpired (SystemClock.Default))
 	await credential.RefreshTokenAsync (CancellationToken.None);
 
 var oauth2 = new SaslMechanismOAuth2 (credential.UserId, credential.Token.AccessToken);