Allow admins to require a manual approval process before new accounts can be used (using MSC3866) (#13556)

synapse/api/constants.py

@@ -269,3 +269,14 @@ class PublicRoomsFilterFields:
 
     GENERIC_SEARCH_TERM: Final = "generic_search_term"
     ROOM_TYPES: Final = "room_types"
+
+
+class ApprovalNoticeMedium:
+    """Identifier for the medium this server will use to serve notice of approval for a
+    specific user's registration.
+
+    As defined in https://github.com/matrix-org/matrix-spec-proposals/blob/babolivier/m_not_approved/proposals/3866-user-not-approved-error.md
+    """
+
+    NONE = "org.matrix.msc3866.none"
+    EMAIL = "org.matrix.msc3866.email"

synapse/api/errors.py

@@ -106,6 +106,8 @@ class Codes(str, Enum):
     # Part of MSC3895.
     UNABLE_DUE_TO_PARTIAL_STATE = "ORG.MATRIX.MSC3895_UNABLE_DUE_TO_PARTIAL_STATE"
 
+    USER_AWAITING_APPROVAL = "ORG.MATRIX.MSC3866_USER_AWAITING_APPROVAL"
+
 
 class CodeMessageException(RuntimeError):
     """An exception with integer code and message string attributes.
@@ -566,6 +568,20 @@ class UnredactedContentDeletedError(SynapseError):
         return cs_error(self.msg, self.errcode, **extra)
 
 
+class NotApprovedError(SynapseError):
+    def __init__(
+        self,
+        msg: str,
+        approval_notice_medium: str,
+    ):
+        super().__init__(
+            code=403,
+            msg=msg,
+            errcode=Codes.USER_AWAITING_APPROVAL,
+            additional_fields={"approval_notice_medium": approval_notice_medium},
+        )
+
+
 def cs_error(msg: str, code: str = Codes.UNKNOWN, **kwargs: Any) -> "JsonDict":
     """Utility method for constructing an error response for client-server
     interactions.