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Improve SAML error messages (#8248)

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Patrick Cloke 2020-09-14 09:05:36 -04:00 • committed by GitHub
parent 04cc249b43
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9 changed files with 178 additions and 185 deletions
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169
synapse/handlers/saml_handler.py
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@ -21,9 +21,10 @@ import saml2
import saml2.response
from saml2.client import Saml2Client
from synapse.api.errors import AuthError, SynapseError
from synapse.api.errors import SynapseError
from synapse.config import ConfigError
from synapse.config.saml2_config import SamlAttributeRequirement
from synapse.http.server import respond_with_html
from synapse.http.servlet import parse_string
from synapse.http.site import SynapseRequest
from synapse.module_api import ModuleApi
@ -41,6 +42,10 @@ if TYPE_CHECKING:
logger = logging.getLogger(__name__)
class MappingException(Exception):
"""Used to catch errors when mapping the SAML2 response to a user."""
@attr.s
class Saml2SessionData:
"""Data we track about SAML2 sessions"""
@ -68,6 +73,7 @@ class SamlHandler:
hs.config.saml2_grandfathered_mxid_source_attribute
)
self._saml2_attribute_requirements = hs.config.saml2.attribute_requirements
self._error_template = hs.config.sso_error_template
# plugin to do custom mapping from saml response to mxid
self._user_mapping_provider = hs.config.saml2_user_mapping_provider_class(
@ -84,6 +90,25 @@ class SamlHandler:
# a lock on the mappings
self._mapping_lock = Linearizer(name="saml_mapping", clock=self._clock)
def _render_error(
self, request, error: str, error_description: Optional[str] = None
) -> None:
"""Render the error template and respond to the request with it.
This is used to show errors to the user. The template of this page can
be found under `synapse/res/templates/sso_error.html`.
Args:
request: The incoming request from the browser.
We'll respond with an HTML page describing the error.
error: A technical identifier for this error.
error_description: A human-readable description of the error.
"""
html = self._error_template.render(
error=error, error_description=error_description
)
respond_with_html(request, 400, html)
def handle_redirect_request(
self, client_redirect_url: bytes, ui_auth_session_id: Optional[str] = None
) -> bytes:
@ -134,49 +159,6 @@ class SamlHandler:
# the dict.
self.expire_sessions()
# Pull out the user-agent and IP from the request.
user_agent = request.requestHeaders.getRawHeaders(b"User-Agent", default=[b""])[
0
].decode("ascii", "surrogateescape")
ip_address = self.hs.get_ip_from_request(request)
user_id, current_session = await self._map_saml_response_to_user(
resp_bytes, relay_state, user_agent, ip_address
)
# Complete the interactive auth session or the login.
if current_session and current_session.ui_auth_session_id:
await self._auth_handler.complete_sso_ui_auth(
user_id, current_session.ui_auth_session_id, request
)
else:
await self._auth_handler.complete_sso_login(user_id, request, relay_state)
async def _map_saml_response_to_user(
self,
resp_bytes: str,
client_redirect_url: str,
user_agent: str,
ip_address: str,
) -> Tuple[str, Optional[Saml2SessionData]]:
"""
Given a sample response, retrieve the cached session and user for it.
Args:
resp_bytes: The SAML response.
client_redirect_url: The redirect URL passed in by the client.
user_agent: The user agent of the client making the request.
ip_address: The IP address of the client making the request.
Returns:
Tuple of the user ID and SAML session associated with this response.
Raises:
SynapseError if there was a problem with the response.
RedirectException: some mapping providers may raise this if they need
to redirect to an interstitial page.
"""
try:
saml2_auth = self._saml_client.parse_authn_request_response(
resp_bytes,
@ -189,12 +171,23 @@ class SamlHandler:
# 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))
raise SynapseError(400, "Unexpected SAML2 login.")
self._render_error(
request, "unsolicited_response", "Unexpected SAML2 login."
)
return
except Exception as e:
raise SynapseError(400, "Unable to parse SAML2 response: %s." % (e,))
self._render_error(
request,
"invalid_response",
"Unable to parse SAML2 response: %s." % (e,),
)
return
if saml2_auth.not_signed:
raise SynapseError(400, "SAML2 response was not signed.")
self._render_error(
request, "unsigned_respond", "SAML2 response was not signed."
)
return
logger.debug("SAML2 response: %s", saml2_auth.origxml)
for assertion in saml2_auth.assertions:
@ -213,15 +206,73 @@ class SamlHandler:
saml2_auth.in_response_to, None
)
# Ensure that the attributes of the logged in user meet the required
# attributes.
for requirement in self._saml2_attribute_requirements:
_check_attribute_requirement(saml2_auth.ava, requirement)
if not _check_attribute_requirement(saml2_auth.ava, requirement):
self._render_error(
request, "unauthorised", "You are not authorised to log in here."
)
return
# Pull out the user-agent and IP from the request.
user_agent = request.requestHeaders.getRawHeaders(b"User-Agent", default=[b""])[
0
].decode("ascii", "surrogateescape")
ip_address = self.hs.get_ip_from_request(request)
# Call the mapper to register/login the user
try:
user_id = await self._map_saml_response_to_user(
saml2_auth, relay_state, user_agent, ip_address
)
except MappingException as e:
logger.exception("Could not map user")
self._render_error(request, "mapping_error", str(e))
return
# Complete the interactive auth session or the login.
if current_session and current_session.ui_auth_session_id:
await self._auth_handler.complete_sso_ui_auth(
user_id, current_session.ui_auth_session_id, request
)
else:
await self._auth_handler.complete_sso_login(user_id, request, relay_state)
async def _map_saml_response_to_user(
self,
saml2_auth: saml2.response.AuthnResponse,
client_redirect_url: str,
user_agent: str,
ip_address: str,
) -> str:
"""
Given a SAML response, retrieve the user ID for it and possibly register the user.
Args:
saml2_auth: The parsed SAML2 response.
client_redirect_url: The redirect URL passed in by the client.
user_agent: The user agent of the client making the request.
ip_address: The IP address of the client making the request.
Returns:
The user ID associated with this response.
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._user_mapping_provider.get_remote_user_id(
saml2_auth, client_redirect_url
)
if not remote_user_id:
raise Exception("Failed to extract remote user id from SAML response")
raise MappingException(
"Failed to extract remote user id from SAML response"
)
with (await self._mapping_lock.queue(self._auth_provider_id)):
# first of all, check if we already have a mapping for this user
@ -235,7 +286,7 @@ class SamlHandler:
)
if registered_user_id is not None:
logger.info("Found existing mapping %s", registered_user_id)
return registered_user_id, current_session
return registered_user_id
# backwards-compatibility hack: see if there is an existing user with a
# suitable mapping from the uid
@ -260,7 +311,7 @@ class SamlHandler:
await self._datastore.record_user_external_id(
self._auth_provider_id, remote_user_id, registered_user_id
)
return registered_user_id, current_session
return registered_user_id
# Map saml response to user attributes using the configured mapping provider
for i in range(1000):
@ -277,7 +328,7 @@ class SamlHandler:
localpart = attribute_dict.get("mxid_localpart")
if not localpart:
raise Exception(
raise MappingException(
"Error parsing SAML2 response: SAML mapping provider plugin "
"did not return a mxid_localpart value"
)
@ -294,8 +345,8 @@ class SamlHandler:
else:
# Unable to generate a username in 1000 iterations
# Break and return error to the user
raise SynapseError(
500, "Unable to generate a Matrix ID from the SAML response"
raise MappingException(
"Unable to generate a Matrix ID from the SAML response"
)
logger.info("Mapped SAML user to local part %s", localpart)
@ -310,7 +361,7 @@ class SamlHandler:
await self._datastore.record_user_external_id(
self._auth_provider_id, remote_user_id, registered_user_id
)
return registered_user_id, current_session
return registered_user_id
def expire_sessions(self):
expire_before = self._clock.time_msec() - self._saml2_session_lifetime
@ -323,11 +374,11 @@ class SamlHandler:
del self._outstanding_requests_dict[reqid]
def _check_attribute_requirement(ava: dict, req: SamlAttributeRequirement):
def _check_attribute_requirement(ava: dict, req: SamlAttributeRequirement) -> bool:
values = ava.get(req.attribute, [])
for v in values:
if v == req.value:
return
return True
logger.info(
"SAML2 attribute %s did not match required value '%s' (was '%s')",
@ -335,7 +386,7 @@ def _check_attribute_requirement(ava: dict, req: SamlAttributeRequirement):
req.value,
values,
)
raise AuthError(403, "You are not authorized to log in here.")
return False
DOT_REPLACE_PATTERN = re.compile(
@ -390,7 +441,7 @@ class DefaultSamlMappingProvider:
return saml_response.ava["uid"][0]
except KeyError:
logger.warning("SAML2 response lacks a 'uid' attestation")
raise SynapseError(400, "'uid' not in SAML2 response")
raise MappingException("'uid' not in SAML2 response")
def saml_response_to_user_attributes(
self,