Combine the CAS & SAML implementations for required attributes. (#9326)

3 files changed, 86 insertions, 51 deletions

diff --git a/synapse/handlers/cas_handler.py b/synapse/handlers/cas_handler.py
index bd35d1fb87..81ed44ac87 100644
--- a/synapse/handlers/cas_handler.py
+++ b/synapse/handlers/cas_handler.py
@@ -14,7 +14,7 @@
 # limitations under the License.
 import logging
 import urllib.parse
-from typing import TYPE_CHECKING, Dict, Optional
+from typing import TYPE_CHECKING, Dict, List, Optional
 from xml.etree import ElementTree as ET
 
 import attr
@@ -49,7 +49,7 @@ class CasError(Exception):
 @attr.s(slots=True, frozen=True)
 class CasResponse:
     username = attr.ib(type=str)
-    attributes = attr.ib(type=Dict[str, Optional[str]])
+    attributes = attr.ib(type=Dict[str, List[Optional[str]]])
 
 
 class CasHandler:
@@ -169,7 +169,7 @@ class CasHandler:
 
         # Iterate through the nodes and pull out the user and any extra attributes.
         user = None
-        attributes = {}
+        attributes = {}  # type: Dict[str, List[Optional[str]]]
         for child in root[0]:
             if child.tag.endswith("user"):
                 user = child.text
@@ -182,7 +182,7 @@ class CasHandler:
                     tag = attribute.tag
                     if "}" in tag:
                         tag = tag.split("}")[1]
-                    attributes[tag] = attribute.text
+                    attributes.setdefault(tag, []).append(attribute.text)
 
         # Ensure a user was found.
         if user is None:
@@ -303,29 +303,10 @@ class CasHandler:
 
         # Ensure that the attributes of the logged in user meet the required
         # attributes.
-        for required_attribute, required_value in self._cas_required_attributes.items():
-            # If required attribute was not in CAS Response - Forbidden
-            if required_attribute not in cas_response.attributes:
-                self._sso_handler.render_error(
-                    request,
-                    "unauthorised",
-                    "You are not authorised to log in here.",
-                    401,
-                )
-                return
-
-            # Also need to check value
-            if required_value is not None:
-                actual_value = cas_response.attributes[required_attribute]
-                # If required attribute value does not match expected - Forbidden
-                if required_value != actual_value:
-                    self._sso_handler.render_error(
-                        request,
-                        "unauthorised",
-                        "You are not authorised to log in here.",
-                        401,
-                    )
-                    return
+        if not self._sso_handler.check_required_attributes(
+            request, cas_response.attributes, self._cas_required_attributes
+        ):
+            return
 
         # Call the mapper to register/login the user
 
@@ -372,9 +353,10 @@ class CasHandler:
             if failures:
                 raise RuntimeError("CAS is not expected to de-duplicate Matrix IDs")
 
+            # Arbitrarily use the first attribute found.
             display_name = cas_response.attributes.get(
-                self._cas_displayname_attribute, None
-            )
+                self._cas_displayname_attribute, [None]
+            )[0]
 
             return UserAttributes(localpart=localpart, display_name=display_name)
 
diff --git a/synapse/handlers/saml_handler.py b/synapse/handlers/saml_handler.py
index e88fd59749..78f130e152 100644
--- a/synapse/handlers/saml_handler.py
+++ b/synapse/handlers/saml_handler.py
@@ -23,7 +23,6 @@ from saml2.client import Saml2Client
 
 from synapse.api.errors import SynapseError
 from synapse.config import ConfigError
-from synapse.config.saml2_config import SamlAttributeRequirement
 from synapse.handlers._base import BaseHandler
 from synapse.handlers.sso import MappingException, UserAttributes
 from synapse.http.servlet import parse_string
@@ -239,12 +238,10 @@ class SamlHandler(BaseHandler):
 
         # Ensure that the attributes of the logged in user meet the required
         # attributes.
-        for requirement in self._saml2_attribute_requirements:
-            if not _check_attribute_requirement(saml2_auth.ava, requirement):
-                self._sso_handler.render_error(
-                    request, "unauthorised", "You are not authorised to log in here."
-                )
-                return
+        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:
@@ -373,21 +370,6 @@ class SamlHandler(BaseHandler):
             del self._outstanding_requests_dict[reqid]
 
 
-def _check_attribute_requirement(ava: dict, req: SamlAttributeRequirement) -> bool:
-    values = ava.get(req.attribute, [])
-    for v in values:
-        if v == req.value:
-            return True
-
-    logger.info(
-        "SAML2 attribute %s did not match required value '%s' (was '%s')",
-        req.attribute,
-        req.value,
-        values,
-    )
-    return False
-
-
 DOT_REPLACE_PATTERN = re.compile(
     ("[^%s]" % (re.escape("".join(mxid_localpart_allowed_characters)),))
 )
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index 96ccd991ed..a63fd52485 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -16,10 +16,12 @@ import abc
 import logging
 from typing import (
     TYPE_CHECKING,
+    Any,
     Awaitable,
     Callable,
     Dict,
     Iterable,
+    List,
     Mapping,
     Optional,
     Set,
@@ -34,6 +36,7 @@ from twisted.web.iweb import IRequest
 
 from synapse.api.constants import LoginType
 from synapse.api.errors import Codes, NotFoundError, RedirectException, SynapseError
+from synapse.config.sso import SsoAttributeRequirement
 from synapse.handlers.ui_auth import UIAuthSessionDataConstants
 from synapse.http import get_request_user_agent
 from synapse.http.server import respond_with_html, respond_with_redirect
@@ -893,6 +896,41 @@ class SsoHandler:
             logger.info("Expiring mapping session %s", session_id)
             del self._username_mapping_sessions[session_id]
 
+    def check_required_attributes(
+        self,
+        request: SynapseRequest,
+        attributes: Mapping[str, List[Any]],
+        attribute_requirements: Iterable[SsoAttributeRequirement],
+    ) -> bool:
+        """
+        Confirm that the required attributes were present in the SSO response.
+
+        If all requirements are met, this will return True.
+
+        If any requirement is not met, then the request will be finalized by
+        showing an error page to the user and False will be returned.
+
+        Args:
+            request: The request to (potentially) respond to.
+            attributes: The attributes from the SSO IdP.
+            attribute_requirements: The requirements that attributes must meet.
+
+        Returns:
+            True if all requirements are met, False if any attribute fails to
+            meet the requirement.
+
+        """
+        # Ensure that the attributes of the logged in user meet the required
+        # attributes.
+        for requirement in attribute_requirements:
+            if not _check_attribute_requirement(attributes, requirement):
+                self.render_error(
+                    request, "unauthorised", "You are not authorised to log in here."
+                )
+                return False
+
+        return True
+
 
 def get_username_mapping_session_cookie_from_request(request: IRequest) -> str:
     """Extract the session ID from the cookie
@@ -903,3 +941,36 @@ def get_username_mapping_session_cookie_from_request(request: IRequest) -> str:
     if not session_id:
         raise SynapseError(code=400, msg="missing session_id")
     return session_id.decode("ascii", errors="replace")
+
+
+def _check_attribute_requirement(
+    attributes: Mapping[str, List[Any]], req: SsoAttributeRequirement
+) -> bool:
+    """Check if SSO attributes meet the proper requirements.
+
+    Args:
+        attributes: A mapping of attributes to an iterable of one or more values.
+        requirement: The configured requirement to check.
+
+    Returns:
+        True if the required attribute was found and had a proper value.
+    """
+    if req.attribute not in attributes:
+        logger.info("SSO attribute missing: %s", req.attribute)
+        return False
+
+    # If the requirement is None, the attribute existing is enough.
+    if req.value is None:
+        return True
+
+    values = attributes[req.attribute]
+    if req.value in values:
+        return True
+
+    logger.info(
+        "SSO attribute %s did not match required value '%s' (was '%s')",
+        req.attribute,
+        req.value,
+        values,
+    )
+    return False