Absolutely 
But since this is not a hosting related question, it might make sense to have it answered here so other people can benefit from the answer as well.
The “add HTML tag” method should be sufficient. The redirect_uri_mismatch error you’re getting now is actually a different error and it means that you have successfully tackled the first challenge.
This error means that you have entered the wrong value in #4 here
It should be https://forum.*yourname*.org/auth/google_auth2/callback
where you obviously substitute *yourname* with the actual value.