Authentication based on return value of external program?

[Steffen Weber]

Hello,

I´m wondering whether there exists a module that makes it possible to
grant authentiation based upon the return value of an external programm.

I know that in general it is not such a great idea to rely upon an
external program, but for not-critical services like for example FTP
being able to implement the authentication backend in PHP, Python or
whatever would be great.

Steffen