slixmpp/sleekxmpp/features/feature_mechanisms/mechanisms.py

"""
    SleekXMPP: The Sleek XMPP Library
    Copyright (C) 2011  Nathanael C. Fritz
    This file is part of SleekXMPP.

    See the file LICENSE for copying permission.
"""

import ssl
import logging

from sleekxmpp.util import sasl
from sleekxmpp.util.stringprep_profiles import StringPrepError
from sleekxmpp.stanza import StreamFeatures
from sleekxmpp.xmlstream import RestartStream, register_stanza_plugin
from sleekxmpp.plugins import BasePlugin
from sleekxmpp.xmlstream.matcher import MatchXPath
from sleekxmpp.xmlstream.handler import Callback
from sleekxmpp.features.feature_mechanisms import stanza


log = logging.getLogger(__name__)


class FeatureMechanisms(BasePlugin):

    name = 'feature_mechanisms'
    description = 'RFC 6120: Stream Feature: SASL'
    dependencies = set()
    stanza = stanza
    default_config = {
        'use_mech': None,
        'use_mechs': None,
        'min_mech': None,
        'sasl_callback': None,
        'security_callback': None,
        'encrypted_plain': True,
        'unencrypted_plain': False,
        'unencrypted_digest': False,
        'unencrypted_cram': False,
        'unencrypted_scram': True,
        'order': 100
    }

    def plugin_init(self):
        if self.sasl_callback is None:
            self.sasl_callback = self._default_credentials

        if self.security_callback is None:
            self.security_callback = self._default_security

        creds = self.sasl_callback(set(['username']), set())
        if not self.use_mech and not creds['username']:
            self.use_mech = 'ANONYMOUS'

        self.mech = None
        self.mech_list = set()
        self.attempted_mechs = set()

        register_stanza_plugin(StreamFeatures, stanza.Mechanisms)

        self.xmpp.register_stanza(stanza.Success)
        self.xmpp.register_stanza(stanza.Failure)
        self.xmpp.register_stanza(stanza.Auth)
        self.xmpp.register_stanza(stanza.Challenge)
        self.xmpp.register_stanza(stanza.Response)
        self.xmpp.register_stanza(stanza.Abort)

        self.xmpp.register_handler(
                Callback('SASL Success',
                         MatchXPath(stanza.Success.tag_name()),
                         self._handle_success,
                         instream=True))
        self.xmpp.register_handler(
                Callback('SASL Failure',
                         MatchXPath(stanza.Failure.tag_name()),
                         self._handle_fail,
                         instream=True))
        self.xmpp.register_handler(
                Callback('SASL Challenge',
                         MatchXPath(stanza.Challenge.tag_name()),
                         self._handle_challenge))

        self.xmpp.register_feature('mechanisms',
                self._handle_sasl_auth,
                restart=True,
                order=self.order)

    def _default_credentials(self, required_values, optional_values):
        creds = self.xmpp.credentials
        result = {}
        values = required_values.union(optional_values)
        for value in values:
            if value == 'username':
                result[value] = creds.get('username', self.xmpp.requested_jid.user)
            elif value == 'email':
                jid = self.xmpp.requested_jid.bare
                result[value] = creds.get('email', jid)
            elif value == 'channel_binding':
                if hasattr(self.xmpp.socket, 'get_channel_binding'):
                    result[value] = self.xmpp.socket.get_channel_binding()
                else:
                    log.debug("Channel binding not supported.")
                    log.debug("Use Python 3.3+ for channel binding and " + \
                              "SCRAM-SHA-1-PLUS support")
                    result[value] = None
            elif value == 'host':
                result[value] = creds.get('host', self.xmpp.requested_jid.domain)
            elif value == 'realm':
                result[value] = creds.get('realm', self.xmpp.requested_jid.domain)
            elif value == 'service-name':
                result[value] = creds.get('service-name', self.xmpp._service_name)
            elif value == 'service':
                result[value] = creds.get('service', 'xmpp')
            elif value in creds:
                result[value] = creds[value]
        return result

    def _default_security(self, values):
        result = {}
        for value in values:
            if value == 'encrypted':
                if 'starttls' in self.xmpp.features:
                    result[value] = True
                elif isinstance(self.xmpp.socket, ssl.SSLSocket):
                    result[value] = True
                else:
                    result[value] = False
            else:
                result[value] = self.config.get(value, False)
        return result

    def _handle_sasl_auth(self, features):
        """
        Handle authenticating using SASL.

        Arguments:
            features -- The stream features stanza.
        """
        if 'mechanisms' in self.xmpp.features:
            # SASL authentication has already succeeded, but the
            # server has incorrectly offered it again.
            return False

        enforce_limit = False
        limited_mechs = self.use_mechs

        if limited_mechs is None:
            limited_mechs = set()
        elif limited_mechs and not isinstance(limited_mechs, set):
            limited_mechs = set(limited_mechs)
            enforce_limit = True

        if self.use_mech:
            limited_mechs.add(self.use_mech)
            enforce_limit = True

        if enforce_limit:
            self.use_mechs = limited_mechs

        self.mech_list = set(features['mechanisms'])

        return self._send_auth()

    def _send_auth(self):
        mech_list = self.mech_list - self.attempted_mechs
        try:
            self.mech = sasl.choose(mech_list,
                                    self.sasl_callback,
                                    self.security_callback,
                                    limit=self.use_mechs,
                                    min_mech=self.min_mech)
        except sasl.SASLNoAppropriateMechanism:
            log.error("No appropriate login method.")
            self.xmpp.event("no_auth", direct=True)
            self.xmpp.event("failed_auth", direct=True)
            self.attempted_mechs = set()
            return self.xmpp.disconnect()
        except StringPrepError:
            log.exception("A credential value did not pass SASLprep.")
            self.xmpp.disconnect()

        resp = stanza.Auth(self.xmpp)
        resp['mechanism'] = self.mech.name
        try:
            resp['value'] = self.mech.process()
        except sasl.SASLCancelled:
            self.attempted_mechs.add(self.mech.name)
            self._send_auth()
        except sasl.SASLMutualAuthFailed:
            log.error("Mutual authentication failed! " + \
                      "A security breach is possible.")
            self.attempted_mechs.add(self.mech.name)
            self.xmpp.disconnect()
        except sasl.SASLFailed:
            self.attempted_mechs.add(self.mech.name)
            self._send_auth()
        else:
            resp.send(now=True)

        return True

    def _handle_challenge(self, stanza):
        """SASL challenge received. Process and send response."""
        resp = self.stanza.Response(self.xmpp)
        try:
            resp['value'] = self.mech.process(stanza['value'])
        except sasl.SASLCancelled:
            self.stanza.Abort(self.xmpp).send()
        except sasl.SASLMutualAuthFailed:
            log.error("Mutual authentication failed! " + \
                      "A security breach is possible.")
            self.attempted_mechs.add(self.mech.name)
            self.xmpp.disconnect()
        except sasl.SASLFailed:
            self.stanza.Abort(self.xmpp).send()
        else:
            if resp.get_value() == '':
                resp.del_value()
            resp.send(now=True)

    def _handle_success(self, stanza):
        """SASL authentication succeeded. Restart the stream."""
        try:
            final = self.mech.process(stanza['value'])
        except sasl.SASLMutualAuthFailed:
            log.error("Mutual authentication failed! " + \
                      "A security breach is possible.")
            self.attempted_mechs.add(self.mech.name)
            self.xmpp.disconnect()
        else:
            self.attempted_mechs = set()
            self.xmpp.authenticated = True
            self.xmpp.features.add('mechanisms')
            self.xmpp.event('auth_success', stanza, direct=True)
            raise RestartStream()

    def _handle_fail(self, stanza):
        """SASL authentication failed. Disconnect and shutdown."""
        self.attempted_mechs.add(self.mech.name)
        log.info("Authentication failed: %s", stanza['condition'])
        self.xmpp.event("failed_auth", stanza, direct=True)
        self._send_auth()
        return True