Building a proper API

Hi there,

I am currently building an api which will grow as time progresses.
for the moment the connection must be only be made by sending over POST var.
eg. site.com/api/file.php

There is a whole bunch of check regarding the key which need to be sent over etc… and will generate a random token for each connection.

Is this right??

How can i make users go to site.com/something - i would like to avoid showing the .php.

I also heard of OAuth. do i really need to use it or not.

Thanks for all the help,

Regards,

Jerome