PAM out should fail with a CompatError

[adiroiban]

Look why PAM was still attempted on Alpine

---

          After installing SFTPPlus to launch as root, with default configuration (and adding `alpinista` as the OS group allowed for file transfer), I get this error below.  (This is default Alpine Linux with no PAM.)

2025-03-31T14:51:54+03:00 20059 Process Unknown 127.0.0.1:51898 Internal error. Failed to authenticate "alpinista". Traceback: <class 'AttributeError'>: Symbol not found: pam_start
/opt/sftppath/lib/python3.12/site-packages/twisted/internet/defer.py:209:maybeDeferred
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:130:requestAvatarId
/opt/sftppath/lib/python3.12/site-packages/twisted/internet/defer.py:2256:unwindGenerator
/opt/sftppath/lib/python3.12/site-packages/twisted/internet/defer.py:2168:_cancellableInlineCallbacks
--- <exception caught here> ---
/opt/sftppath/lib/python3.12/site-packages/twisted/internet/defer.py:2000:_inlineCallbacks
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:208:_requestAvatarId
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:337:_authenticate
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/os.py:401:authenticate
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/os.py:597:_validateOSUser
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:880:validate
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:904:_validate
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:928:_validatePassword
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:1015:_validateOSPassword
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:1038:_validateWithPAMOnly
/opt/sftppath/lib/python3.12/site-packages/chevah_compat/unix_users.py:225:pamWithUsernameAndPassword
/opt/sftppath/lib/python3.12/site-packages/pam/__init__.py:130:authenticate
/opt/sftppath/lib/python3.12/site-packages/pam/__internals.py:206:__init__
/opt/sftppath/lib/python3.12/ctypes/__init__.py:392:__getattr__
/opt/sftppath/lib/python3.12/ctypes/__init__.py:397:__getitem__
2025-03-31T14:51:54+03:00 40000 https-1 Unknown 127.0.0.1:51898 Unauthorized request for "/__chsps__/login". Authentication failed. Contact your administrator for more details.
2025-03-31T14:52:27+03:00 20059 Process Unknown 127.0.0.1:51898 Internal error. Failed to authenticate "alpinista". Traceback: <class 'AttributeError'>: Symbol not found: pam_start
/opt/sftppath/lib/python3.12/site-packages/twisted/internet/defer.py:209:maybeDeferred
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:130:requestAvatarId
/opt/sftppath/lib/python3.12/site-packages/twisted/internet/defer.py:2256:unwindGenerator
/opt/sftppath/lib/python3.12/site-packages/twisted/internet/defer.py:2168:_cancellableInlineCallbacks
--- <exception caught here> ---
/opt/sftppath/lib/python3.12/site-packages/twisted/internet/defer.py:2000:_inlineCallbacks
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:208:_requestAvatarId
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:337:_authenticate
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/os.py:401:authenticate
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/os.py:597:_validateOSUser
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:880:validate
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:904:_validate
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:928:_validatePassword
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:1015:_validateOSPassword
/opt/sftppath/lib/python3.12/site-packages/chevah/server/authentication/credential_checker.py:1038:_validateWithPAMOnly
/opt/sftppath/lib/python3.12/site-packages/chevah_compat/unix_users.py:225:pamWithUsernameAndPassword
/opt/sftppath/lib/python3.12/site-packages/pam/__init__.py:130:authenticate
/opt/sftppath/lib/python3.12/site-packages/pam/__internals.py:206:__init__
/opt/sftppath/lib/python3.12/ctypes/__init__.py:392:__getattr__
/opt/sftppath/lib/python3.12/ctypes/__init__.py:397:__getitem__

Originally posted by @dumol in https://github.com/chevah/server/issues/7042#issuecomment-2766001056