Currently, if you enable GoogleLogin and disable all other primaryauth providers (such as LocalPasswordAuthenticationProvider and the TemporarayPasswordAuthenticationProvider) you get a login form like this:
The "Log in" button is pretty useless, as it always returns "Credentials could not be authenticated". So the form is now more confusing as helping, as the only way to login is with the GoogleLogin button.
Personally, I'm not sure, how or if we could fix this easily, because it seems there is a variaty of possible input options, some may need this button, some may not. But probably we could, maybe, check, if all AuthenticationRequests return buttons only (as far as I can imagine, this would represent providers that need these buttons only?!). Or maybe someone else has a better idea :]