text: # Copyright 2019 The Matrix.org Foundation C.I.C.
  #
  # 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.
  import logging
  import re
  from typing import TYPE_CHECKING, Callable, Dict, Optional, Set, Tuple
  
  import attr
  import saml2
  import saml2.response
  from saml2.client import Saml2Client
  
  from synapse.api.errors import SynapseError
  from synapse.config import ConfigError
  from synapse.handlers.sso import MappingException, UserAttributes
  from synapse.http.servlet import parse_string
  from synapse.http.site import SynapseRequest
  from synapse.module_api import ModuleApi
  from synapse.types import (
      UserID,
      map_username_to_mxid_localpart,
      mxid_localpart_allowed_characters,
  )
  from synapse.util.iterutils import chunk_seq
  
  if TYPE_CHECKING:
      from synapse.server import HomeServer
  
  logger = logging.getLogger(__name__)
  
  
  @attr.s(slots=True, auto_attribs=True)
  class Saml2SessionData:
      """Data we track about SAML2 sessions"""
  
      # time the session was created, in milliseconds
      creation_time: int
      # The user interactive authentication session ID associated with this SAML
      # session (or None if this SAML session is for an initial login).
      ui_auth_session_id: Optional[str] = None
  
  
  class SamlHandler:
      def __init__(self, hs: "HomeServer"):
          self.store = hs.get_datastores().main
          self.clock = hs.get_clock()
          self.server_name = hs.hostname
          self._saml_client = Saml2Client(hs.config.saml2.saml2_sp_config)
          self._saml_idp_entityid = hs.config.saml2.saml2_idp_entityid
  
          self._saml2_session_lifetime = hs.config.saml2.saml2_session_lifetime
          self._grandfathered_mxid_source_attribute = (
              hs.config.saml2.saml2_grandfathered_mxid_source_attribute
          )
          self._saml2_attribute_requirements = hs.config.saml2.attribute_requirements
  
          # plugin to do custom mapping from saml response to mxid
          self._user_mapping_provider = hs.config.saml2.saml2_user_mapping_provider_class(
              hs.config.saml2.saml2_user_mapping_provider_config,
              ModuleApi(hs, hs.get_auth_handler()),
          )
  
          # identifier for the external_ids table
          self.idp_id = "saml"
  
          # user-facing name of this auth provider
          self.idp_name = "SAML"
  
          # we do not currently support icons/brands for SAML auth, but this is required by
          # the SsoIdentityProvider protocol type.
          self.idp_icon = None
          self.idp_brand = None
  
          # a map from saml session id to Saml2SessionData object
          self._outstanding_requests_dict: Dict[str, Saml2SessionData] = {}
  
          self._sso_handler = hs.get_sso_handler()
          self._sso_handler.register_identity_provider(self)
  
      async def handle_redirect_request(
          self,
          request: SynapseRequest,
          client_redirect_url: Optional[bytes],
          ui_auth_session_id: Optional[str] = None,
      ) -> str:
          """Handle an incoming request to /login/sso/redirect
  
          Args:
              request: the incoming HTTP request
              client_redirect_url: the URL that we should redirect the
                  client to after login (or None for UI Auth).
              ui_auth_session_id: The session ID of the ongoing UI Auth (or
                  None if this is a login).
  
          Returns:
              URL to redirect to
          """
          if not client_redirect_url:
              # Some SAML identity providers (e.g. Google) require a
              # RelayState parameter on requests, so pass in a dummy redirect URL
              # (which will never get used).
              client_redirect_url = b"unused"
  
          reqid, info = self._saml_client.prepare_for_authenticate(
              entityid=self._saml_idp_entityid, relay_state=client_redirect_url
          )
  
          # Since SAML sessions timeout it is useful to log when they were created.
          logger.info("Initiating a new SAML session: %s" % (reqid,))
  
          now = self.clock.time_msec()
          self._outstanding_requests_dict[reqid] = Saml2SessionData(
              creation_time=now,
              ui_auth_session_id=ui_auth_session_id,
          )
  
          for key, value in info["headers"]:
              if key == "Location":
                  return value
  
          # this shouldn't happen!
          raise Exception("prepare_for_authenticate didn't return a Location header")
  
      async def handle_saml_response(self, request: SynapseRequest) -> None:
          """Handle an incoming request to /_synapse/client/saml2/authn_response
  
          Args:
              request: the incoming request from the browser. We'll
                  respond to it with a redirect.
  
          Returns:
              Completes once we have handled the request.
          """
          resp_bytes = parse_string(request, "SAMLResponse", required=True)
          relay_state = parse_string(request, "RelayState", required=True)
  
          # expire outstanding sessions before parse_authn_request_response checks
          # the dict.
          self.expire_sessions()
  
          try:
              saml2_auth = self._saml_client.parse_authn_request_response(
                  resp_bytes,
                  saml2.BINDING_HTTP_POST,
                  outstanding=self._outstanding_requests_dict,
              )
          except saml2.response.UnsolicitedResponse as e:
              # the pysaml2 library helpfully logs an ERROR here, but neglects to log
              # the session ID. I don't really want to put the full text of the exception
              # in the (user-visible) exception message, so let's log the exception here
              # so we can track down the session IDs later.
              logger.warning(str(e))
              self._sso_handler.render_error(
                  request, "unsolicited_response", "Unexpected SAML2 login."
              )
              return
          except Exception as e:
              self._sso_handler.render_error(
                  request,
                  "invalid_response",
                  "Unable to parse SAML2 response: %s." % (e,),
              )
              return
  
          if saml2_auth.not_signed:
              self._sso_handler.render_error(
                  request, "unsigned_respond", "SAML2 response was not signed."
              )
              return
  
          logger.debug("SAML2 response: %s", saml2_auth.origxml)
  
          await self._handle_authn_response(request, saml2_auth, relay_state)
  
      async def _handle_authn_response(
          self,
          request: SynapseRequest,
          saml2_auth: saml2.response.AuthnResponse,
          relay_state: str,
      ) -> None:
          """Handle an AuthnResponse, having parsed it from the request params
  
          Assumes that the signature on the response object has been checked. Maps
          the user onto an MXID, registering them if necessary, and returns a response
          to the browser.
  
          Args:
              request: the incoming request from the browser. We'll respond to it with an
                  HTML page or a redirect
              saml2_auth: the parsed AuthnResponse object
              relay_state: the RelayState query param, which encodes the URI to rediret
                 back to
          """
  
          for assertion in saml2_auth.assertions:
              # kibana limits the length of a log field, whereas this is all rather
              # useful, so split it up.
              count = 0
              for part in chunk_seq(str(assertion), 10000):
                  logger.info(
                      "SAML2 assertion: %s%s", "(%i)..." % (count,) if count else "", part
                  )
                  count += 1
  
          logger.info("SAML2 mapped attributes: %s", saml2_auth.ava)
  
          current_session = self._outstanding_requests_dict.pop(
              saml2_auth.in_response_to, None
          )
  
          # first check if we're doing a UIA
          if current_session and current_session.ui_auth_session_id:
              try:
                  remote_user_id = self._remote_id_from_saml_response(saml2_auth, None)
              except MappingException as e:
                  logger.exception("Failed to extract remote user id from SAML response")
                  self._sso_handler.render_error(request, "mapping_error", str(e))
                  return
  
              return await self._sso_handler.complete_sso_ui_auth_request(
                  self.idp_id,
                  remote_user_id,
                  current_session.ui_auth_session_id,
                  request,
              )
  
          # otherwise, we're handling a login request.
  
          # Ensure that the attributes of the logged in user meet the required
          # attributes.
          if not self._sso_handler.check_required_attributes(
              request, saml2_auth.ava, self._saml2_attribute_requirements
          ):
              return
  
          # Call the mapper to register/login the user
          try:
              await self._complete_saml_login(saml2_auth, request, relay_state)
          except MappingException as e:
              logger.exception("Could not map user")
              self._sso_handler.render_error(request, "mapping_error", str(e))
  
      async def _complete_saml_login(
          self,
          saml2_auth: saml2.response.AuthnResponse,
          request: SynapseRequest,
          client_redirect_url: str,
      ) -> None:
          """
          Given a SAML response, complete the login flow
  
          Retrieves the remote user ID, registers the user if necessary, and serves
          a redirect back to the client with a login-token.
  
          Args:
              saml2_auth: The parsed SAML2 response.
              request: The request to respond to
              client_redirect_url: The redirect URL passed in by the client.
  
          Raises:
              MappingException if there was a problem mapping the response to a user.
              RedirectException: some mapping providers may raise this if they need
                  to redirect to an interstitial page.
          """
          remote_user_id = self._remote_id_from_saml_response(
              saml2_auth, client_redirect_url
          )
  
          async def saml_response_to_remapped_user_attributes(
              failures: int,
          ) -> UserAttributes:
              """
              Call the mapping provider to map a SAML response to user attributes and coerce the result into the standard form.
  
              This is backwards compatibility for abstraction for the SSO handler.
              """
              # Call the mapping provider.
              result = self._user_mapping_provider.saml_response_to_user_attributes(
                  saml2_auth, failures, client_redirect_url
              )
              # Remap some of the results.
              return UserAttributes(
                  localpart=result.get("mxid_localpart"),
                  display_name=result.get("displayname"),
                  emails=result.get("emails", []),
              )
  
          async def grandfather_existing_users() -> Optional[str]:
              # backwards-compatibility hack: see if there is an existing user with a
              # suitable mapping from the uid
              if (
                  self._grandfathered_mxid_source_attribute
                  and self._grandfathered_mxid_source_attribute in saml2_auth.ava
              ):
                  attrval = saml2_auth.ava[self._grandfathered_mxid_source_attribute][0]
                  user_id = UserID(
                      map_username_to_mxid_localpart(attrval), self.server_name
                  ).to_string()
  
                  logger.debug(
                      "Looking for existing account based on mapped %s %s",
                      self._grandfathered_mxid_source_attribute,
                      user_id,
                  )
  
                  users = await self.store.get_users_by_id_case_insensitive(user_id)
                  if users:
                      registered_user_id = list(users.keys())[0]
                      logger.info("Grandfathering mapping to %s", registered_user_id)
                      return registered_user_id
  
              return None
  
          await self._sso_handler.complete_sso_login_request(
              self.idp_id,
              remote_user_id,
              request,
              client_redirect_url,
              saml_response_to_remapped_user_attributes,
              grandfather_existing_users,
          )
  
      def _remote_id_from_saml_response(
          self,
          saml2_auth: saml2.response.AuthnResponse,
          client_redirect_url: Optional[str],
      ) -> str:
          """Extract the unique remote id from a SAML2 AuthnResponse
  
          Args:
              saml2_auth: The parsed SAML2 response.
              client_redirect_url: The redirect URL passed in by the client.
          Returns:
              remote user id
  
          Raises:
              MappingException if there was an error extracting the user id
          """
          # It's not obvious why we need to pass in the redirect URI to the mapping
          # provider, but we do :/
          remote_user_id = self._user_mapping_provider.get_remote_user_id(
              saml2_auth, client_redirect_url
          )
  
          if not remote_user_id:
              raise MappingException(
                  "Failed to extract remote user id from SAML response"
              )
  
          return remote_user_id
  
      def expire_sessions(self) -> None:
          expire_before = self.clock.time_msec() - self._saml2_session_lifetime
          to_expire = set()
          for reqid, data in self._outstanding_requests_dict.items():
              if data.creation_time < expire_before:
                  to_expire.add(reqid)
          for reqid in to_expire:
              logger.debug("Expiring session id %s", reqid)
              del self._outstanding_requests_dict[reqid]
  
  
  DOT_REPLACE_PATTERN = re.compile(
      "[^%s]" % (re.escape("".join(mxid_localpart_allowed_characters)),)
  )
  
  
  def dot_replace_for_mxid(username: str) -> str:
      """Replace any characters which are not allowed in Matrix IDs with a dot."""
      username = username.lower()
      username = DOT_REPLACE_PATTERN.sub(".", username)
  
      # regular mxids aren't allowed to start with an underscore either
      username = re.sub("^_", "", username)
      return username
  
  
  MXID_MAPPER_MAP: Dict[str, Callable[[str], str]] = {
      "hexencode": map_username_to_mxid_localpart,
      "dotreplace": dot_replace_for_mxid,
  }
  
  
  @attr.s(auto_attribs=True)
  class SamlConfig:
      mxid_source_attribute: str
      mxid_mapper: Callable[[str], str]
  
  
  class DefaultSamlMappingProvider:
      __version__ = "0.0.1"
  
      def __init__(self, parsed_config: SamlConfig, module_api: ModuleApi):
          """The default SAML user mapping provider
  
          Args:
              parsed_config: Module configuration
              module_api: module api proxy
          """
          self._mxid_source_attribute = parsed_config.mxid_source_attribute
          self._mxid_mapper = parsed_config.mxid_mapper
  
          self._grandfathered_mxid_source_attribute = (
              module_api._hs.config.saml2.saml2_grandfathered_mxid_source_attribute
          )
  
      def get_remote_user_id(
          self, saml_response: saml2.response.AuthnResponse, client_redirect_url: str
      ) -> str:
          """Extracts the remote user id from the SAML response"""
          try:
              return saml_response.ava["uid"][0]
          except KeyError:
              logger.warning("SAML2 response lacks a 'uid' attestation")
              raise MappingException("'uid' not in SAML2 response")
  
      def saml_response_to_user_attributes(
          self,
          saml_response: saml2.response.AuthnResponse,
          failures: int,
          client_redirect_url: str,
      ) -> dict:
          """Maps some text from a SAML response to attributes of a new user
  
          Args:
              saml_response: A SAML auth response object
  
              failures: How many times a call to this function with this
                  saml_response has resulted in a failure
  
              client_redirect_url: where the client wants to redirect to
  
          Returns:
              dict: A dict containing new user attributes. Possible keys:
                  * mxid_localpart (str): Required. The localpart of the user's mxid
                  * displayname (str): The displayname of the user
                  * emails (list[str]): Any emails for the user
          """
          try:
              mxid_source = saml_response.ava[self._mxid_source_attribute][0]
          except KeyError:
              logger.warning(
                  "SAML2 response lacks a '%s' attestation",
                  self._mxid_source_attribute,
              )
              raise SynapseError(
                  400, "%s not in SAML2 response" % (self._mxid_source_attribute,)
              )
  
          # Use the configured mapper for this mxid_source
          localpart = self._mxid_mapper(mxid_source)
  
          # Append suffix integer if last call to this function failed to produce
          # a usable mxid.
          localpart += str(failures) if failures else ""
  
          # Retrieve the display name from the saml response
          # If displayname is None, the mxid_localpart will be used instead
          displayname = saml_response.ava.get("displayName", [None])[0]
  
          # Retrieve any emails present in the saml response
          emails = saml_response.ava.get("email", [])
  
          return {
              "mxid_localpart": localpart,
              "displayname": displayname,
              "emails": emails,
          }
  
      @staticmethod
      def parse_config(config: dict) -> SamlConfig:
          """Parse the dict provided by the homeserver's config
          Args:
              config: A dictionary containing configuration options for this provider
          Returns:
              SamlConfig: A custom config object for this module
          """
          # Parse config options and use defaults where necessary
          mxid_source_attribute = config.get("mxid_source_attribute", "uid")
          mapping_type = config.get("mxid_mapping", "hexencode")
  
          # Retrieve the associating mapping function
          try:
              mxid_mapper = MXID_MAPPER_MAP[mapping_type]
          except KeyError:
              raise ConfigError(
                  "saml2_config.user_mapping_provider.config: '%s' is not a valid "
                  "mxid_mapping value" % (mapping_type,)
              )
  
          return SamlConfig(mxid_source_attribute, mxid_mapper)
  
      @staticmethod
      def get_saml_attributes(config: SamlConfig) -> Tuple[Set[str], Set[str]]:
          """Returns the required attributes of a SAML
  
          Args:
              config: A SamlConfig object containing configuration params for this provider
  
          Returns:
              The first set equates to the saml auth response
                  attributes that are required for the module to function, whereas the
                  second set consists of those attributes which can be used if
                  available, but are not necessary
          """
          return {"uid", config.mxid_source_attribute}, {"displayName", "email"}
  