I'm currently developing an authentication module for an application. The decision was made to do this by using PAM. I have made this work but it can only authenticate the user that started the application.
This means that if I started the application as the user 'appname' the authentication only tells me it is successful if the user is 'appname' and not 'some_user'
If I su to that 'some_user' and started the application in that terminal then I can authenticate 'some_user' but not 'appname'
I turned on the debug flag for pam_unix in common-auth. Resulting in the following output when it rejects:
unix_chkpwd: check pass; user unknown unix_chkpwd: password check failed for user (pamtest) [app]: pam_unix(other:auth): authentication failure; logname=[appname] uid=1000 euid=1000 tty= ruser=[appname] rhost= user=pamtest