#!/usr/bin/env python
from os import path
from crypt import crypt
from re import compile as compile_regex
def check_auth(user, password):
"""Perform authentication against the local systme.
This function will perform authentication against the local system's
/etc/shadow or /etc/passwd database for a given user and password.
:param user: The username to perform authentication with
:type user: str
:param password: The password (plain text) for the given user
:type password: str
:returns: True if successful, None otherwise.
:rtype: True or None
"""
salt_pattern = compile_regex(r"\$.*\$.*\$")
passwd = "/etc/shadow" if path.exists("/etc/shadow") else "/etc/passwd"
with open(passwd, "r") as f:
rows = (line.strip().split(":") for line in f)
records = [row for row in rows if row[0] == user]
hash = records and records[0][1]
salt = salt_pattern.match(hash).group()
return crypt(password, salt) == hash
