Function allowed_to_send_state_event 

pub(crate) async fn allowed_to_send_state_event(
    services: &Services,
    sender: &UserId,
    room_id: &RoomId,
    event_type: &StateEventType,
    state_key: &str,
    json: &Raw<AnyStateEventContent>,
) -> Result

Applies the server’s policy for sending a state event, before the room lock.

Refuses what room auth alone would allow but this server forbids: changes to m.room.create, a server ACL that would lock this server out, admin room exposure, foreign aliases, and membership changes the sender is barred from.