"Why the hell would i allow Google or f...ing Facebook to sign in as me to another site?"
Some people are unaware of the problems or just pain don't care. You don't need to use those, you can use github or openid (which as you know you can host yourself).
"because this is a security nightmare waiting to happen."
You are behind the times, it's already happened :P
"If not, then i'll have to think about alternative solutions, like restart my webpage-modifying proxy project to filter out all the clutter and make metacpan more readable."
It'd make more sense to work with the existing codebase and provide a PR for the functionality you discuss, then others could collaborate/get the benefits.