python-pam

Python pam module supporting py3 for Linux type systems (!windows)

Security

See SECURITY.md for supported versions and how to report vulnerabilities.

Threading and concurrency

pam.authenticate() is safe to call from many threads at once. Each call uses its own PAM handle; libpam ctypes bindings are loaded once and shared (no global lock on the auth path).

Do not share a single PamAuthenticator / pam.pam() instance across threads without external synchronization. That object owns mutable PAM session state (handle, code, reason, messages). For sessions (call_end=False), keep one instance per thread (or serialize access).

High-QPS login APIs should use:

import pam

if pam.authenticate(username, password, service='myapp'):
    ...

Credentials (resetcreds)

After a successful pam_authenticate + pam_acct_mgmt, authenticate() calls pam_setcred(..., PAM_REINITIALIZE_CRED) when resetcreds=True (the default).

Keep the default (True) when this process is acting like a login / credential handoff: modules may establish or refresh credentials (e.g. Kerberos), and you care about that step succeeding as part of auth.

Set resetcreds=False when you only need to verify a username/password (typical web/API “is this password valid?” checks). You are not assuming the user’s identity or opening a session; skipping setcred avoids extra module work and avoids treating a setcred failure as an authentication failure.

# Password check only
pam.authenticate(user, password, service='myapp', resetcreds=False)

# Login-style / credential-aware stack (default)
pam.authenticate(user, password, service='login')

Examples

Commandline example:

[david@Scott python-pam]$ python pam/pam.py
Username: david
Password:
Auth result: Success (0)
Pam Environment List item: XDG_SEAT=seat0
Pam Environment item: XDG_SEAT=seat0
Missing Pam Environment item: asdf=None
Open session: Success (0)
Close session: Success (0)

Inline examples:

>>> import pam
>>> pam.authenticate('david', 'correctpassword')
True
>>> p = pam.pam()
>>> p.authenticate('david', 'correctpassword')
True
>>> p.authenticate('david', 'badpassword')
False
>>> p.authenticate('david', 'correctpassword', service='login')
True
>>> p.authenticate('david', 'correctpassword', service='unknownservice')
False
>>> p.authenticate('david', 'correctpassword', service='login', resetcreds=True)
True
>>> p.authenticate('david', 'correctpassword', encoding='latin-1')
True
>>> print('{} {}'.format(p.code, p.reason))
0 Success
>>> p.authenticate('david', 'badpassword')
False
>>> print('{} {}'.format(p.code, p.reason))
7 Authentication failure
>>>

Authentication and privileges

Please note, python-pam and all tools that do authentication follow two rules:

• You have root (or privileged access): you can check any account's password for validity
• You don't have root: you can only check the validity of the username running the tool

If you need to authenticate multiple users, you must use an authentication stack that at some stage has privileged access. On Linux systems one example of doing this is using SSSD.

Typical Linux installations check against /etc/shadow with pam_unix.so which will spawn /usr/bin/unix_chkpwd to verify the password. Both of these are intentionally written to meet the above two rules. You can test the functionality of unix_chkpwd in the following manner:

Replace good with the correct password, replace david with your appropriate username.

~$ mkfifo /tmp/myfifo

~$ (echo -ne 'good\0' > /tmp/myfifo & /usr/bin/unix_chkpwd david nullok < /tmp/myfifo ) ; echo $?
0

~$ (echo -ne 'bad\0' > /tmp/myfifo & /usr/bin/unix_chkpwd david nullok < /tmp/myfifo ) ; echo $?
7

~$ (echo -ne 'good\0' > /tmp/myfifo & /usr/bin/unix_chkpwd someotheruser nullok < /tmp/myfifo ) ; echo $?
9