Can you not just make the format of your default login different from that of the client? W/o knowing more details, take this with a grain of salt. BUT, I wou

Can you not just make the format of your default login different from that of the client? W/o knowing more details, take this with a grain of salt. BUT, I would just have the standard user/pass login form, and let your backend do the heavy lifting (figure out the login type from the format, or from trying to login with one method first). Don't put it on the user to choose. This should be simple enough to do with some backend magic.