Using diameter aaa protocol with nginx

I want to set up a AAA layer over the nginx server (for approxiamtely
users at a time). I saw the available options, and found diameter and
tacacs+ to be the best. I found there’s a PAM module/library for
implementing tacacs+ with nginx. Is there a similar module for Diameter
it is more suitable for my requirements? If not what is the procedure to
integrate tacacs+ with nginx. I am using Ubuntu 14.04.