Add config for customizing the claim used for JWT logins. (#11361)

Allows specifying a different claim (from the default "sub") to use
when calculating the localpart of the Matrix ID used during the
JWT login.

2 files changed, 11 insertions, 1 deletions

diff --git a/synapse/config/jwt.py b/synapse/config/jwt.py
index 9d295f5856..24c3ef01fc 100644
--- a/synapse/config/jwt.py
+++ b/synapse/config/jwt.py
@@ -31,6 +31,8 @@ class JWTConfig(Config):
             self.jwt_secret = jwt_config["secret"]
             self.jwt_algorithm = jwt_config["algorithm"]
 
+            self.jwt_subject_claim = jwt_config.get("subject_claim", "sub")
+
             # The issuer and audiences are optional, if provided, it is asserted
             # that the claims exist on the JWT.
             self.jwt_issuer = jwt_config.get("issuer")
@@ -46,6 +48,7 @@ class JWTConfig(Config):
             self.jwt_enabled = False
             self.jwt_secret = None
             self.jwt_algorithm = None
+            self.jwt_subject_claim = None
             self.jwt_issuer = None
             self.jwt_audiences = None
 
@@ -88,6 +91,12 @@ class JWTConfig(Config):
             #
             #algorithm: "provided-by-your-issuer"
 
+            # Name of the claim containing a unique identifier for the user.
+            #
+            # Optional, defaults to `sub`.
+            #
+            #subject_claim: "sub"
+
             # The issuer to validate the "iss" claim against.
             #
             # Optional, if provided the "iss" claim will be required and
diff --git a/synapse/rest/client/login.py b/synapse/rest/client/login.py
index 467444a041..00e65c66ac 100644
--- a/synapse/rest/client/login.py
+++ b/synapse/rest/client/login.py
@@ -72,6 +72,7 @@ class LoginRestServlet(RestServlet):
         # JWT configuration variables.
         self.jwt_enabled = hs.config.jwt.jwt_enabled
         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
@@ -413,7 +414,7 @@ class LoginRestServlet(RestServlet):
                 errcode=Codes.FORBIDDEN,
             )
 
-        user = payload.get("sub", None)
+        user = payload.get(self.jwt_subject_claim, None)
         if user is None:
             raise LoginError(403, "Invalid JWT", errcode=Codes.FORBIDDEN)