wp_login action can't deal with alternate auth mechanisms

[Otto42]

In the wp_signon function, the action hook for wp_login in called like this:
do_action('wp_login', $credentialsuser_login?);

Problem is that $credentialsuser_login? is the content of the form field passed to it by the login screen. If an alternate authentication mechanism is used (like via Twitter or Facebook), then the action does not get the resulting user name that is logging in.

Fix:

If the $user variable is_a WP_User object, then the value passed to this action hook should be $user->user_login instead, so as to pass the login name of the authenticated user to the action.