#!/usr/bin/python

# Copyright (c) 2013 Red Hat, Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Requires the following command to be run:
#   setsebool -P httpd_can_network_connect 1
#   setsebool -P httpd_can_network_memcache 1

import cgi
from swift.common.memcached import MemcacheRing
import os
import grp
import random
import re
import subprocess
from time import time, ctime

# After how many seconds the cached information about an authentication
# token is discarded.
TOKEN_LIFE = 86400

# This is used as a prefix for tokens and memcache keys. We use the default
# value from the Swift tempauth filter. In the future, this should be turned
# into a configuration parameter.
RESELLER_PREFIX = 'AUTH_'

MEMCACHE_SERVERS = ['127.0.0.1:11211']

DEBUG_HEADERS = True


def main():
    remote_user = os.environ['REMOTE_USER']
    matches = re.match('([^@]+)@.*', remote_user)
    if not matches:
        raise RuntimeError("Malformed REMOTE_USER \"%s\"" % remote_user)

    username = matches.group(1)

    mc = MemcacheRing(MEMCACHE_SERVERS)

    # Check if we already got a token for this user.
    memcache_user_key = '%s/user/%s' % (RESELLER_PREFIX, username)
    token = None
    candidate_token = mc.get(memcache_user_key)
    if candidate_token:
        memcache_token_key = '%s/token/%s' % (RESELLER_PREFIX, candidate_token)
        cached_auth_data = mc.get(memcache_token_key)
        if cached_auth_data:
            expires, groups = cached_auth_data
            if expires > time():
                token = candidate_token

    if not token:
        # We don't use uuid.uuid4() here because importing the uuid module
        # causes (harmless) SELinux denials in the audit log on RHEL 6. If this
        # is a security concern, a custom SELinux policy module could be
        # written to not log those denials.
        r = random.SystemRandom()
        token = '%stk%s' % \
                (RESELLER_PREFIX,
                 ''.join(r.choice('abcdef0123456789') for x in range(32)))

        # Retrieve the numerical group IDs. We cannot list the group names
        # because group names from Active Directory may contain spaces, and
        # we wouldn't be able to split the list of group names into its
        # elements.
        p = subprocess.Popen(['id', '-G', username], stdout=subprocess.PIPE)
        if p.wait() != 0:
            raise RuntimeError("Failure running id -G for %s" % remote_user)

        (p_stdout, p_stderr) = p.communicate()

        # Convert the group numbers into group names.
        groups = []
        for gid in p_stdout.strip().split(" "):
            groups.append(grp.getgrgid(int(gid))[0])

        # The first element of the list is considered a unique identifier
        # for the user. We add the username to accomplish this.
        if username in groups:
            groups.remove(username)
        groups = [username] + groups

        groups = ','.join(groups)

        expires = time() + TOKEN_LIFE
        auth_data = (expires, groups)

        memcache_token_key = "%s/token/%s" % (RESELLER_PREFIX, token)
        mc.set(memcache_token_key, auth_data, timeout=TOKEN_LIFE)

        # Record the token with the user info for future use.
        memcache_user_key = '%s/user/%s' % (RESELLER_PREFIX, username)
        mc.set(memcache_user_key, token, timeout=TOKEN_LIFE)

    print "X-Auth-Token: %s" % token

    # For debugging.
    if DEBUG_HEADERS:
        print "X-Debug-Remote-User: %s" % username
        print "X-Debug-Groups: %s" % groups
        print "X-Debug-Token-Life: %ss" % TOKEN_LIFE
        print "X-Debug-Token-Expires: %s" % ctime(expires)

    print ""

try:
    print("Content-Type: text/html")
    main()
except:
    cgi.print_exception()