Hello Lukas,
IBM provides a free access to AIX cloud servers together with your choice of OS to port your application. I've used the service some years back and it works really well. The free service is intended to encourage porting of applications to AIX. Here is a link:
Just pick your hardware platform, OS and server memory/disk requirements and the server is configured for you. You then connect remotely using VPN and upload your code and compile/test.
At present we are using different solutions for Linux (older PAM modules and moving to SSSD) and AIX (commercial product, but prefer to standardize on SSSD if that becomes an option).
On a side note - I'm looking to do some testing with SSSD and ad_provider in the coming week on FreeBSD/PCBSD. I've only found notes of ldap provider examples, but would like to adapt and document ad_provider functionality.
Cheers,
Frank Pikelner