#!/usr/bin/python

# Requires the python-memcached package to be installed.
#
# Requires the following command to be run:
#   setsebool -P httpd_can_network_connect 1
#   setsebool -P httpd_can_network_memcache 1

import cgi
import json
from memcached import MemcacheRing
import os
import random
import re
import subprocess
from time import time

# 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 = ['rhs1.example.com:11211']

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\n" % token

    # For debugging.
    print "<pre>%i / %s</pre>" % mc.get(memcache_token_key)

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