Title: #871: pam: set PAM_USER properly with allow_missing_name
Currently if the allow_missing_name pam_sss option is used PAM_USER is
set to the fully-qualified name only for the files provider it is set to
the short name. This might cause issue with other components expecting
that the value of PAM_USER corresponds to the name returned by the nss
calls getpwnam() and getpwuid().
With this patch PAM_USER is set to the same user name as returned by the
NSS responder. For the communication between pam_sss and SSSD's PAM
responder the fully-qualified name is kept.
Related to https://pagure.io/SSSD/sssd/issue/4069
To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/871/head:pr871
git checkout pr871