I have an idea, but I'm not sure if it would be a security risk.
Let the user pick a username to go with the ID provider. When you fill in the username, it'll look up (AJAX) which provider was used and offer/highlight that one?
The question is, is it a security risk if anyone can type in any username to find out which ID provider it is used with?
Let the user pick a username to go with the ID provider. When you fill in the username, it'll look up (AJAX) which provider was used and offer/highlight that one?
The question is, is it a security risk if anyone can type in any username to find out which ID provider it is used with?