Record the SSO Auth Provider in the login token (#9510)

This great big stack of commits is a a whole load of hoop-jumping to make it easier to store additional values in login tokens, and then to actually store the SSO Identity Provider in the login token. (Making use of that data will follow in a subsequent PR.)

7 files changed, 201 insertions, 101 deletions

diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 89e62b0e36..968cf6f174 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -39,6 +39,7 @@ from synapse.logging import opentracing as opentracing
 from synapse.storage.databases.main.registration import TokenLookupResult
 from synapse.types import StateMap, UserID
 from synapse.util.caches.lrucache import LruCache
+from synapse.util.macaroons import get_value_from_macaroon, satisfy_expiry
 from synapse.util.metrics import Measure
 
 logger = logging.getLogger(__name__)
@@ -408,7 +409,7 @@ class Auth:
             raise _InvalidMacaroonException()
 
         try:
-            user_id = self.get_user_id_from_macaroon(macaroon)
+            user_id = get_value_from_macaroon(macaroon, "user_id")
 
             guest = False
             for caveat in macaroon.caveats:
@@ -416,7 +417,12 @@ class Auth:
                     guest = True
 
             self.validate_macaroon(macaroon, rights, user_id=user_id)
-        except (pymacaroons.exceptions.MacaroonException, TypeError, ValueError):
+        except (
+            pymacaroons.exceptions.MacaroonException,
+            KeyError,
+            TypeError,
+            ValueError,
+        ):
             raise InvalidClientTokenError("Invalid macaroon passed.")
 
         if rights == "access":
@@ -424,27 +430,6 @@ class Auth:
 
         return user_id, guest
 
-    def get_user_id_from_macaroon(self, macaroon):
-        """Retrieve the user_id given by the caveats on the macaroon.
-
-        Does *not* validate the macaroon.
-
-        Args:
-            macaroon (pymacaroons.Macaroon): The macaroon to validate
-
-        Returns:
-            (str) user id
-
-        Raises:
-            InvalidClientCredentialsError if there is no user_id caveat in the
-                macaroon
-        """
-        user_prefix = "user_id = "
-        for caveat in macaroon.caveats:
-            if caveat.caveat_id.startswith(user_prefix):
-                return caveat.caveat_id[len(user_prefix) :]
-        raise InvalidClientTokenError("No user caveat in macaroon")
-
     def validate_macaroon(self, macaroon, type_string, user_id):
         """
         validate that a Macaroon is understood by and was signed by this server.
@@ -465,21 +450,13 @@ class Auth:
         v.satisfy_exact("type = " + type_string)
         v.satisfy_exact("user_id = %s" % user_id)
         v.satisfy_exact("guest = true")
-        v.satisfy_general(self._verify_expiry)
+        satisfy_expiry(v, self.clock.time_msec)
 
         # access_tokens include a nonce for uniqueness: any value is acceptable
         v.satisfy_general(lambda c: c.startswith("nonce = "))
 
         v.verify(macaroon, self._macaroon_secret_key)
 
-    def _verify_expiry(self, caveat):
-        prefix = "time < "
-        if not caveat.startswith(prefix):
-            return False
-        expiry = int(caveat[len(prefix) :])
-        now = self.hs.get_clock().time_msec()
-        return now < expiry
-
     def get_appservice_by_req(self, request: SynapseRequest) -> ApplicationService:
         token = self.get_access_token_from_request(request)
         service = self.store.get_app_service_by_token(token)
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index 3978e41518..bec0c615d4 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -65,6 +65,7 @@ from synapse.storage.roommember import ProfileInfo
 from synapse.types import JsonDict, Requester, UserID
 from synapse.util import stringutils as stringutils
 from synapse.util.async_helpers import maybe_awaitable
+from synapse.util.macaroons import get_value_from_macaroon, satisfy_expiry
 from synapse.util.msisdn import phone_number_to_msisdn
 from synapse.util.threepids import canonicalise_email
 
@@ -170,6 +171,16 @@ class SsoLoginExtraAttributes:
     extra_attributes = attr.ib(type=JsonDict)
 
 
+@attr.s(slots=True, frozen=True)
+class LoginTokenAttributes:
+    """Data we store in a short-term login token"""
+
+    user_id = attr.ib(type=str)
+
+    # the SSO Identity Provider that the user authenticated with, to get this token
+    auth_provider_id = attr.ib(type=str)
+
+
 class AuthHandler(BaseHandler):
     SESSION_EXPIRE_MS = 48 * 60 * 60 * 1000
 
@@ -1164,18 +1175,16 @@ class AuthHandler(BaseHandler):
             return None
         return user_id
 
-    async def validate_short_term_login_token_and_get_user_id(self, login_token: str):
-        auth_api = self.hs.get_auth()
-        user_id = None
+    async def validate_short_term_login_token(
+        self, login_token: str
+    ) -> LoginTokenAttributes:
         try:
-            macaroon = pymacaroons.Macaroon.deserialize(login_token)
-            user_id = auth_api.get_user_id_from_macaroon(macaroon)
-            auth_api.validate_macaroon(macaroon, "login", user_id)
+            res = self.macaroon_gen.verify_short_term_login_token(login_token)
         except Exception:
             raise AuthError(403, "Invalid token", errcode=Codes.FORBIDDEN)
 
-        await self.auth.check_auth_blocking(user_id)
-        return user_id
+        await self.auth.check_auth_blocking(res.user_id)
+        return res
 
     async def delete_access_token(self, access_token: str):
         """Invalidate a single access token
@@ -1397,6 +1406,7 @@ class AuthHandler(BaseHandler):
     async def complete_sso_login(
         self,
         registered_user_id: str,
+        auth_provider_id: str,
         request: Request,
         client_redirect_url: str,
         extra_attributes: Optional[JsonDict] = None,
@@ -1406,6 +1416,9 @@ class AuthHandler(BaseHandler):
 
         Args:
             registered_user_id: The registered user ID to complete SSO login for.
+            auth_provider_id: The id of the SSO Identity provider that was used for
+                login. This will be stored in the login token for future tracking in
+                prometheus metrics.
             request: The request to complete.
             client_redirect_url: The URL to which to redirect the user at the end of the
                 process.
@@ -1427,6 +1440,7 @@ class AuthHandler(BaseHandler):
 
         self._complete_sso_login(
             registered_user_id,
+            auth_provider_id,
             request,
             client_redirect_url,
             extra_attributes,
@@ -1437,6 +1451,7 @@ class AuthHandler(BaseHandler):
     def _complete_sso_login(
         self,
         registered_user_id: str,
+        auth_provider_id: str,
         request: Request,
         client_redirect_url: str,
         extra_attributes: Optional[JsonDict] = None,
@@ -1463,7 +1478,7 @@ class AuthHandler(BaseHandler):
 
         # Create a login token
         login_token = self.macaroon_gen.generate_short_term_login_token(
-            registered_user_id
+            registered_user_id, auth_provider_id=auth_provider_id
         )
 
         # Append the login token to the original redirect URL (i.e. with its query
@@ -1569,15 +1584,48 @@ class MacaroonGenerator:
         return macaroon.serialize()
 
     def generate_short_term_login_token(
-        self, user_id: str, duration_in_ms: int = (2 * 60 * 1000)
+        self,
+        user_id: str,
+        auth_provider_id: str,
+        duration_in_ms: int = (2 * 60 * 1000),
     ) -> str:
         macaroon = self._generate_base_macaroon(user_id)
         macaroon.add_first_party_caveat("type = login")
         now = self.hs.get_clock().time_msec()
         expiry = now + duration_in_ms
         macaroon.add_first_party_caveat("time < %d" % (expiry,))
+        macaroon.add_first_party_caveat("auth_provider_id = %s" % (auth_provider_id,))
         return macaroon.serialize()
 
+    def verify_short_term_login_token(self, token: str) -> LoginTokenAttributes:
+        """Verify a short-term-login macaroon
+
+        Checks that the given token is a valid, unexpired short-term-login token
+        minted by this server.
+
+        Args:
+            token: the login token to verify
+
+        Returns:
+            the user_id that this token is valid for
+
+        Raises:
+            MacaroonVerificationFailedException if the verification failed
+        """
+        macaroon = pymacaroons.Macaroon.deserialize(token)
+        user_id = get_value_from_macaroon(macaroon, "user_id")
+        auth_provider_id = get_value_from_macaroon(macaroon, "auth_provider_id")
+
+        v = pymacaroons.Verifier()
+        v.satisfy_exact("gen = 1")
+        v.satisfy_exact("type = login")
+        v.satisfy_general(lambda c: c.startswith("user_id = "))
+        v.satisfy_general(lambda c: c.startswith("auth_provider_id = "))
+        satisfy_expiry(v, self.hs.get_clock().time_msec)
+        v.verify(macaroon, self.hs.config.key.macaroon_secret_key)
+
+        return LoginTokenAttributes(user_id=user_id, auth_provider_id=auth_provider_id)
+
     def generate_delete_pusher_token(self, user_id: str) -> str:
         macaroon = self._generate_base_macaroon(user_id)
         macaroon.add_first_party_caveat("type = delete_pusher")
diff --git a/synapse/handlers/oidc_handler.py b/synapse/handlers/oidc_handler.py
index 07db1e31e4..b4a74390cc 100644
--- a/synapse/handlers/oidc_handler.py
+++ b/synapse/handlers/oidc_handler.py
@@ -42,6 +42,7 @@ from synapse.logging.context import make_deferred_yieldable
 from synapse.types import JsonDict, UserID, map_username_to_mxid_localpart
 from synapse.util import json_decoder
 from synapse.util.caches.cached_call import RetryOnExceptionCachedCall
+from synapse.util.macaroons import get_value_from_macaroon, satisfy_expiry
 
 if TYPE_CHECKING:
     from synapse.server import HomeServer
@@ -211,7 +212,7 @@ class OidcHandler:
             session_data = self._token_generator.verify_oidc_session_token(
                 session, state
             )
-        except (MacaroonDeserializationException, ValueError) as e:
+        except (MacaroonDeserializationException, KeyError) as e:
             logger.exception("Invalid session for OIDC callback")
             self._sso_handler.render_error(request, "invalid_session", str(e))
             return
@@ -745,7 +746,7 @@ class OidcProvider:
                 idp_id=self.idp_id,
                 nonce=nonce,
                 client_redirect_url=client_redirect_url.decode(),
-                ui_auth_session_id=ui_auth_session_id,
+                ui_auth_session_id=ui_auth_session_id or "",
             ),
         )
 
@@ -1020,10 +1021,9 @@ class OidcSessionTokenGenerator:
         macaroon.add_first_party_caveat(
             "client_redirect_url = %s" % (session_data.client_redirect_url,)
         )
-        if session_data.ui_auth_session_id:
-            macaroon.add_first_party_caveat(
-                "ui_auth_session_id = %s" % (session_data.ui_auth_session_id,)
-            )
+        macaroon.add_first_party_caveat(
+            "ui_auth_session_id = %s" % (session_data.ui_auth_session_id,)
+        )
         now = self._clock.time_msec()
         expiry = now + duration_in_ms
         macaroon.add_first_party_caveat("time < %d" % (expiry,))
@@ -1046,7 +1046,7 @@ class OidcSessionTokenGenerator:
             The data extracted from the session cookie
 
         Raises:
-            ValueError if an expected caveat is missing from the macaroon.
+            KeyError if an expected caveat is missing from the macaroon.
         """
         macaroon = pymacaroons.Macaroon.deserialize(session)
 
@@ -1057,26 +1057,16 @@ class OidcSessionTokenGenerator:
         v.satisfy_general(lambda c: c.startswith("nonce = "))
         v.satisfy_general(lambda c: c.startswith("idp_id = "))
         v.satisfy_general(lambda c: c.startswith("client_redirect_url = "))
-        # Sometimes there's a UI auth session ID, it seems to be OK to attempt
-        # to always satisfy this.
         v.satisfy_general(lambda c: c.startswith("ui_auth_session_id = "))
-        v.satisfy_general(self._verify_expiry)
+        satisfy_expiry(v, self._clock.time_msec)
 
         v.verify(macaroon, self._macaroon_secret_key)
 
         # Extract the session data from the token.
-        nonce = self._get_value_from_macaroon(macaroon, "nonce")
-        idp_id = self._get_value_from_macaroon(macaroon, "idp_id")
-        client_redirect_url = self._get_value_from_macaroon(
-            macaroon, "client_redirect_url"
-        )
-        try:
-            ui_auth_session_id = self._get_value_from_macaroon(
-                macaroon, "ui_auth_session_id"
-            )  # type: Optional[str]
-        except ValueError:
-            ui_auth_session_id = None
-
+        nonce = get_value_from_macaroon(macaroon, "nonce")
+        idp_id = get_value_from_macaroon(macaroon, "idp_id")
+        client_redirect_url = get_value_from_macaroon(macaroon, "client_redirect_url")
+        ui_auth_session_id = get_value_from_macaroon(macaroon, "ui_auth_session_id")
         return OidcSessionData(
             nonce=nonce,
             idp_id=idp_id,
@@ -1084,33 +1074,6 @@ class OidcSessionTokenGenerator:
             ui_auth_session_id=ui_auth_session_id,
         )
 
-    def _get_value_from_macaroon(self, macaroon: pymacaroons.Macaroon, key: str) -> str:
-        """Extracts a caveat value from a macaroon token.
-
-        Args:
-            macaroon: the token
-            key: the key of the caveat to extract
-
-        Returns:
-            The extracted value
-
-        Raises:
-            ValueError: if the caveat was not in the macaroon
-        """
-        prefix = key + " = "
-        for caveat in macaroon.caveats:
-            if caveat.caveat_id.startswith(prefix):
-                return caveat.caveat_id[len(prefix) :]
-        raise ValueError("No %s caveat in macaroon" % (key,))
-
-    def _verify_expiry(self, caveat: str) -> bool:
-        prefix = "time < "
-        if not caveat.startswith(prefix):
-            return False
-        expiry = int(caveat[len(prefix) :])
-        now = self._clock.time_msec()
-        return now < expiry
-
 
 @attr.s(frozen=True, slots=True)
 class OidcSessionData:
@@ -1125,8 +1088,8 @@ class OidcSessionData:
     # The URL the client gave when it initiated the flow. ("" if this is a UI Auth)
     client_redirect_url = attr.ib(type=str)
 
-    # The session ID of the ongoing UI Auth (None if this is a login)
-    ui_auth_session_id = attr.ib(type=Optional[str], default=None)
+    # The session ID of the ongoing UI Auth ("" if this is a login)
+    ui_auth_session_id = attr.ib(type=str)
 
 
 UserAttributeDict = TypedDict(
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index 80e28bdcbe..8a22dab54a 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -456,6 +456,7 @@ class SsoHandler:
 
         await self._auth_handler.complete_sso_login(
             user_id,
+            auth_provider_id,
             request,
             client_redirect_url,
             extra_login_attributes,
@@ -886,6 +887,7 @@ class SsoHandler:
 
         await self._auth_handler.complete_sso_login(
             user_id,
+            session.auth_provider_id,
             request,
             session.client_redirect_url,
             session.extra_login_attributes,
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index db2d400b7e..781e02fbbb 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -203,11 +203,26 @@ class ModuleApi:
         )
 
     def generate_short_term_login_token(
-        self, user_id: str, duration_in_ms: int = (2 * 60 * 1000)
+        self,
+        user_id: str,
+        duration_in_ms: int = (2 * 60 * 1000),
+        auth_provider_id: str = "",
     ) -> str:
-        """Generate a login token suitable for m.login.token authentication"""
+        """Generate a login token suitable for m.login.token authentication
+
+        Args:
+            user_id: gives the ID of the user that the token is for
+
+            duration_in_ms: the time that the token will be valid for
+
+            auth_provider_id: the ID of the SSO IdP that the user used to authenticate
+               to get this token, if any. This is encoded in the token so that
+               /login can report stats on number of successful logins by IdP.
+        """
         return self._hs.get_macaroon_generator().generate_short_term_login_token(
-            user_id, duration_in_ms
+            user_id,
+            auth_provider_id,
+            duration_in_ms,
         )
 
     @defer.inlineCallbacks
@@ -276,6 +291,7 @@ class ModuleApi:
         """
         self._auth_handler._complete_sso_login(
             registered_user_id,
+            "<unknown>",
             request,
             client_redirect_url,
         )
@@ -286,6 +302,7 @@ class ModuleApi:
         request: SynapseRequest,
         client_redirect_url: str,
         new_user: bool = False,
+        auth_provider_id: str = "<unknown>",
     ):
         """Complete a SSO login by redirecting the user to a page to confirm whether they
         want their access token sent to `client_redirect_url`, or redirect them to that
@@ -299,9 +316,15 @@ class ModuleApi:
                 redirect them directly if whitelisted).
             new_user: set to true to use wording for the consent appropriate to a user
                 who has just registered.
+            auth_provider_id: the ID of the SSO IdP which was used to log in. This
+                is used to track counts of sucessful logins by IdP.
         """
         await self._auth_handler.complete_sso_login(
-            registered_user_id, request, client_redirect_url, new_user=new_user
+            registered_user_id,
+            auth_provider_id,
+            request,
+            client_redirect_url,
+            new_user=new_user,
         )
 
     @defer.inlineCallbacks
diff --git a/synapse/rest/client/v1/login.py b/synapse/rest/client/v1/login.py
index 925edfc402..1ec3a47ffb 100644
--- a/synapse/rest/client/v1/login.py
+++ b/synapse/rest/client/v1/login.py
@@ -283,12 +283,10 @@ class LoginRestServlet(RestServlet):
         """
         token = login_submission["token"]
         auth_handler = self.auth_handler
-        user_id = await auth_handler.validate_short_term_login_token_and_get_user_id(
-            token
-        )
+        res = await auth_handler.validate_short_term_login_token(token)
 
         return await self._complete_login(
-            user_id, login_submission, self.auth_handler._sso_login_callback
+            res.user_id, login_submission, self.auth_handler._sso_login_callback
         )
 
     async def _do_jwt_login(self, login_submission: JsonDict) -> Dict[str, str]:
diff --git a/synapse/util/macaroons.py b/synapse/util/macaroons.py
new file mode 100644
index 0000000000..12cdd53327
--- /dev/null
+++ b/synapse/util/macaroons.py
@@ -0,0 +1,89 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Quentin Gliech
+# Copyright 2021 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.
+
+"""Utilities for manipulating macaroons"""
+
+from typing import Callable, Optional
+
+import pymacaroons
+from pymacaroons.exceptions import MacaroonVerificationFailedException
+
+
+def get_value_from_macaroon(macaroon: pymacaroons.Macaroon, key: str) -> str:
+    """Extracts a caveat value from a macaroon token.
+
+    Checks that there is exactly one caveat of the form "key = <val>" in the macaroon,
+    and returns the extracted value.
+
+    Args:
+        macaroon: the token
+        key: the key of the caveat to extract
+
+    Returns:
+        The extracted value
+
+    Raises:
+        MacaroonVerificationFailedException: if there are conflicting values for the
+             caveat in the macaroon, or if the caveat was not found in the macaroon.
+    """
+    prefix = key + " = "
+    result = None  # type: Optional[str]
+    for caveat in macaroon.caveats:
+        if not caveat.caveat_id.startswith(prefix):
+            continue
+
+        val = caveat.caveat_id[len(prefix) :]
+
+        if result is None:
+            # first time we found this caveat: record the value
+            result = val
+        elif val != result:
+            # on subsequent occurrences, raise if the value is different.
+            raise MacaroonVerificationFailedException(
+                "Conflicting values for caveat " + key
+            )
+
+    if result is not None:
+        return result
+
+    # If the caveat is not there, we raise a MacaroonVerificationFailedException.
+    # Note that it is insecure to generate a macaroon without all the caveats you
+    # might need (because there is nothing stopping people from adding extra caveats),
+    # so if the caveat isn't there, something odd must be going on.
+    raise MacaroonVerificationFailedException("No %s caveat in macaroon" % (key,))
+
+
+def satisfy_expiry(v: pymacaroons.Verifier, get_time_ms: Callable[[], int]) -> None:
+    """Make a macaroon verifier which accepts 'time' caveats
+
+    Builds a caveat verifier which will accept unexpired 'time' caveats, and adds it to
+    the given macaroon verifier.
+
+    Args:
+        v: the macaroon verifier
+        get_time_ms: a callable which will return the timestamp after which the caveat
+            should be considered expired. Normally the current time.
+    """
+
+    def verify_expiry_caveat(caveat: str):
+        time_msec = get_time_ms()
+        prefix = "time < "
+        if not caveat.startswith(prefix):
+            return False
+        expiry = int(caveat[len(prefix) :])
+        return time_msec < expiry
+
+    v.satisfy_general(verify_expiry_caveat)