Service/plugin for VERY large number of users

Hi

I would like to have a member registration on my wordpress site that aims to have millions of users eventually. I don’t think wordpress user registration can handle this, so was wondering if anyone has suggestions for any services that would handle his kind of load.

I would like to capture basic info of the user/member and ideally have that data accessible through an API of some sort to be able to represent it visually.

I’m not a seasoned developer but I have a little experience.

Thanks