PAM authentication module

I need an opensource module or library to learn how to code for PAM. I install vsFTP and need a PAM module (open source with source code to learn) to help me to call to my server via http to authenticate this access ftp user validate or not. (PAM module send username, password and IP to my server by http protocol). Anyone can help me to install any libabry to do that. userABC -- access to --> vsFTP ----> PAM (must install) ---> Call HTTP server to authenticate the user ABC valid or not. Thank you so much,