I had the opportunity to play with this setup for a few minutes this morning.
** Disclaimer: I am not an Ubuntu, xrdp, gnome, kde expert (however, I'm quite curious).
Basically what I did was to follow the steps outlined on this youtube video. I got it working to the point that I can successfully log in. My desktop won't start, but I figured that I should only try to make authentication work.
Here's the information about the system:
The xrdp-sesman PAM config files includes common-auth, just like you have it outlined.
After installing and rebooting, I first tested with a local user and all was fine. Then I tested with an AD user. Here is the sequence:
1. From my RDP session on my Windows system, I typed in the username/password for the AD user in question (dwirth)
note that this user is not in /etc/passwd, it is an AD user (see adquery user above)
2. Then this window pops-up, and provides a sequence on the back-end:
3. I assume that if my system was configured correctly (which I didn't) the gnome, kde or any other desktop would have been launched correctly. I just get the cursor to play with and a grey/black screen.
Note: This setup needs the vncserver to run, so you also have to make sure that you have it working with PAM as well as your chosen desktop.
I can confirm that as xrdp-sesman goes, all is well with Centrify by looking at the auth.log:
There you have it.
Since there's no bug, I suggest that you tail subscribe to the /var/log/auth.log and look at the sequences.
R.P