Website administration tool to manage multiple sites

I have an admin section in my webapp to manage users and roles (like the website administration tool). My question is : which is the best way to manage users and role for all sites running on a remote server ? The idea is to have a single webapp administration tool on the remote server for all sites without replicate the admin section on each applic开发者_开发百科ation.

Some of you has faced the same problem?