Central indentification management for multiple sites

[Tang Jianwei]

Hi All,

     is there anyone can share some experience of central identification 
management including user/pass, ssh key-pair and OpenVPN certs etc. 
around multiple site?

     I am now looking for such a simplified solution to manage all my 
Ubuntu/Linux servers included system user and OpenVPN certs, any 
suggestion/recommendation will be very appreciated.

     Thank you very much in advance.

Best Regards
Tomas