Do not allow deactivated users to login with JWT. (#15624)

To improve the organization of this code it moves the JWT login
checks to a separate handler and then fixes the bug (and a
deprecation warning).

1 files changed, 118 insertions, 0 deletions

diff --git a/synapse/handlers/jwt.py b/synapse/handlers/jwt.py
new file mode 100644
index 0000000000..5fddc0e315
--- /dev/null
+++ b/synapse/handlers/jwt.py
@@ -0,0 +1,118 @@
+# Copyright 2023 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.
+from typing import TYPE_CHECKING
+
+from authlib.jose import JsonWebToken, JWTClaims
+from authlib.jose.errors import BadSignatureError, InvalidClaimError, JoseError
+
+from synapse.api.errors import Codes, LoginError, StoreError, UserDeactivatedError
+from synapse.types import JsonDict, UserID
+
+if TYPE_CHECKING:
+    from synapse.server import HomeServer
+
+
+class JwtHandler:
+    def __init__(self, hs: "HomeServer"):
+        self.hs = hs
+        self._main_store = hs.get_datastores().main
+
+        self.jwt_secret = hs.config.jwt.jwt_secret
+        self.jwt_subject_claim = hs.config.jwt.jwt_subject_claim
+        self.jwt_algorithm = hs.config.jwt.jwt_algorithm
+        self.jwt_issuer = hs.config.jwt.jwt_issuer
+        self.jwt_audiences = hs.config.jwt.jwt_audiences
+
+    async def validate_login(self, login_submission: JsonDict) -> str:
+        """
+        Authenticates the user for the /login API
+
+        Args:
+            login_submission: the whole of the login submission
+                (including 'type' and other relevant fields)
+
+        Returns:
+            The user ID that is logging in.
+
+        Raises:
+            LoginError if there was an authentication problem.
+        """
+        token = login_submission.get("token", None)
+        if token is None:
+            raise LoginError(
+                403, "Token field for JWT is missing", errcode=Codes.FORBIDDEN
+            )
+
+        jwt = JsonWebToken([self.jwt_algorithm])
+        claim_options = {}
+        if self.jwt_issuer is not None:
+            claim_options["iss"] = {"value": self.jwt_issuer, "essential": True}
+        if self.jwt_audiences is not None:
+            claim_options["aud"] = {"values": self.jwt_audiences, "essential": True}
+
+        try:
+            claims = jwt.decode(
+                token,
+                key=self.jwt_secret,
+                claims_cls=JWTClaims,
+                claims_options=claim_options,
+            )
+        except BadSignatureError:
+            # We handle this case separately to provide a better error message
+            raise LoginError(
+                403,
+                "JWT validation failed: Signature verification failed",
+                errcode=Codes.FORBIDDEN,
+            )
+        except JoseError as e:
+            # A JWT error occurred, return some info back to the client.
+            raise LoginError(
+                403,
+                "JWT validation failed: %s" % (str(e),),
+                errcode=Codes.FORBIDDEN,
+            )
+
+        try:
+            claims.validate(leeway=120)  # allows 2 min of clock skew
+
+            # Enforce the old behavior which is rolled out in productive
+            # servers: if the JWT contains an 'aud' claim but none is
+            # configured, the login attempt will fail
+            if claims.get("aud") is not None:
+                if self.jwt_audiences is None or len(self.jwt_audiences) == 0:
+                    raise InvalidClaimError("aud")
+        except JoseError as e:
+            raise LoginError(
+                403,
+                "JWT validation failed: %s" % (str(e),),
+                errcode=Codes.FORBIDDEN,
+            )
+
+        user = claims.get(self.jwt_subject_claim, None)
+        if user is None:
+            raise LoginError(403, "Invalid JWT", errcode=Codes.FORBIDDEN)
+
+        user_id = UserID(user, self.hs.hostname).to_string()
+
+        # If the account has been deactivated, do not proceed with the login
+        # flow.
+        try:
+            deactivated = await self._main_store.get_user_deactivated_status(user_id)
+        except StoreError:
+            # JWT lazily creates users, so they may not exist in the database yet.
+            deactivated = False
+        if deactivated:
+            raise UserDeactivatedError("This account has been deactivated")
+
+        return user_id