PAM: return short name for files provider users
If the 'allow_missing_name' option is used with pam_sss and the user
name will be determined based on the certificate content and the mapping
rules the PAM responder will by default return the fully-qualified name
of the user which is then later used by other PAM modules as well.
For local users which are configured to use SSSD for Smartcard
authentication this might cause issues in other PAM modules because they
are not aware of the fully-qualified name and will treat the user as
With this patch the PAM responder will return the short name for all
users handled by the files provider.
Related to https://pagure.io/SSSD/sssd/issue/3848
Reviewed-by: Jakub Hrozek <firstname.lastname@example.org>