[SSSD] [sssd PR#479][opened] MAN: Document that auth and access IPA and AD providers rely on id_provider being set to the same type

[jhrozek]

   URL: https://github.com/SSSD/sssd/pull/479
Author: jhrozek
 Title: #479: MAN: Document that auth and access IPA and AD providers rely on id_provider
being set to the same type
Action: opened

PR body:
"""
Resolves: https://pagure.io/SSSD/sssd/issue/3547

The IPA and AD auth and access providers rely (often for performance
reasons) on certain properties that are set during the user or group
resolution with the same provider type.

However, there are users who wish to combine different provider types,
typically to use identities from local UNIX files but authenticate against
a remote server. We should discourage that in our documentation

But at the same time, I think flat our failing would be too harsh...I was
also thinking about printing a DEBUG message during initialization, if the
reviewer thinks this is a good idea, I'll do that as well.
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/479/head:pr479
git checkout pr479