3 files changed, 21 insertions, 2 deletions
diff --git a/synapse/config/oidc.py b/synapse/config/oidc.py
index df8c422043..77c1d1dc8e 100644
--- a/synapse/config/oidc.py
+++ b/synapse/config/oidc.py
@@ -136,6 +136,7 @@ OIDC_PROVIDER_CONFIG_SCHEMA = {
             "type": "array",
             "items": SsoAttributeRequirement.JSON_SCHEMA,
         },
+        "enable_registration": {"type": "boolean"},
     },
 }
 
@@ -306,6 +307,7 @@ def _parse_oidc_config_dict(
         user_mapping_provider_class=user_mapping_provider_class,
         user_mapping_provider_config=user_mapping_provider_config,
         attribute_requirements=attribute_requirements,
+        enable_registration=oidc_config.get("enable_registration", True),
     )
 
 
@@ -405,3 +407,6 @@ class OidcProviderConfig:
 
     # required attributes to require in userinfo to allow login/registration
     attribute_requirements: List[SsoAttributeRequirement]
+
+    # Whether automatic registrations are enabled in the ODIC flow. Defaults to True
+    enable_registration: bool
diff --git a/synapse/handlers/oidc.py b/synapse/handlers/oidc.py
index 0fc829acf7..e7e0b5e049 100644
--- a/synapse/handlers/oidc.py
+++ b/synapse/handlers/oidc.py
@@ -1239,6 +1239,7 @@ class OidcProvider:
             grandfather_existing_users,
             extra_attributes,
             auth_provider_session_id=sid,
+            registration_enabled=self._config.enable_registration,
         )
 
     def _remote_id_from_userinfo(self, userinfo: UserInfo) -> str:
diff --git a/synapse/handlers/sso.py b/synapse/handlers/sso.py
index 4a27c0f051..c28325323c 100644
--- a/synapse/handlers/sso.py
+++ b/synapse/handlers/sso.py
@@ -383,6 +383,7 @@ class SsoHandler:
         grandfather_existing_users: Callable[[], Awaitable[Optional[str]]],
         extra_login_attributes: Optional[JsonDict] = None,
         auth_provider_session_id: Optional[str] = None,
+        registration_enabled: bool = True,
     ) -> None:
         """
         Given an SSO ID, retrieve the user ID for it and possibly register the user.
@@ -435,6 +436,10 @@ class SsoHandler:
 
             auth_provider_session_id: An optional session ID from the IdP.
 
+            registration_enabled: An optional boolean to enable/disable automatic
+            registrations of new users. If false and the user does not exist then the
+            flow is aborted. Defaults to true.
+
         Raises:
             MappingException if there was a problem mapping the response to a user.
             RedirectException: if the mapping provider needs to redirect the user
@@ -462,8 +467,16 @@ class SsoHandler:
                         auth_provider_id, remote_user_id, user_id
                     )
 
-            # Otherwise, generate a new user.
-            if not user_id:
+            if not user_id and not registration_enabled:
+                logger.info(
+                    "User does not exist and registration are disabled for IdP '%s' and remote_user_id '%s'",
+                    auth_provider_id,
+                    remote_user_id,
+                )
+                raise MappingException(
+                    "User does not exist and registrations are disabled"
+                )
+            elif not user_id:  # Otherwise, generate a new user.
                 attributes = await self._call_attribute_mapper(sso_to_matrix_id_mapper)
 
                 next_step_url = self._get_url_for_next_new_user_step(