Hello!
I realized I did not answer your PAM / AD question.
In our rocker 3.6 build, we have used winbind, in the rocker 4.0 (and 4.0.3 now) builds we must use sssd.
I installed the rstudio on centos via the rstudio.com provided rpm file and configured sssd/kerberos/etc. and the login worked fine.
I am not certain yet if the issue is the rocker build chain or the different OS implementations.