Sign Up & Login Porcess

HI Support,

I am planning to migrate a community into a WPMU setup, one of the first things I need to figure out is how to approve people, or make sure that the people given access and allowed to login to the site are actual members of the community.

I am wondering if there is a plugin that allows for review of those creating accounts for the site?

As this is most likely a common issue I was wondering if you could point me to common solutions?

Also, I am looking at setting up an Open ID login option and if you could recommend an Open Id plugin?

Kind Regards,