Login via OpenID

Now this allow user to login via multiple OpenID accounts, I'll implement the web part after this and see if it will confuse the Interface part or I can fix it later if I find using just one account is more suitable. Any idea ? :)
This doc may be helpful for using the extension fields mechanism: https://metacpan.org/pod/Net::OpenID::ClaimedIdentity#cident-set_extension_args-ns_uri-args