Hello. Trying to write a rewrite rule that will transform this url http://external_site.com/login?back_url=http%3A%2F%2Finternal_url%2F to this one http://external_site.com/login?back_url=http%3A%2F%2Fexternal_site.com%2F I know I need to play with arguments and rewrite but I'm stuck.