It's a bad idea.

I use to have this on my website with facebook instead of asking someone to create an account and link it with facebook.

If facebook bans your website => you can't access your account anymore

If facebook crash => you can't access you account anymore

If your facebook account is compromised => you can't access your account anymore

If facebook is blocked on the intranet => you can't ...

there are tons of reason people don't do zero-signup with twitter or facebook.