support hypercorn server_names against dns rebind attacks, add cookie sessions to flash messages

src/capport/comm/hub.py

@@ -339,7 +339,7 @@ class Hub:
             await trio.sleep_forever()
 
     def _calc_authentication(self, ssl_binding: bytes, server_side: bool) -> bytes:
-        m = hmac.new(self._config.secret.encode('utf8'), digestmod=hashlib.sha256)
+        m = hmac.new(self._config.comm_secret.encode('utf8'), digestmod=hashlib.sha256)
         if server_side:
             m.update(b'server$')
         else: