diff --git a/tests/utils.py b/tests/utils.py

index 9bff3ff3b9..63730e7f29 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -197,7 +197,10 @@ class MockHttpResource(HttpServer):
 
     @patch('twisted.web.http.Request')
     @defer.inlineCallbacks
-    def trigger(self, http_method, path, content, mock_request, federation_auth=False):
+    def trigger(
+        self, http_method, path, content, mock_request,
+        federation_auth_origin=None,
+    ):
         """ Fire an HTTP event.
 
         Args:
@@ -206,6 +209,7 @@ class MockHttpResource(HttpServer):
             content : The HTTP body
             mock_request : Mocked request to pass to the event so it can get
                            content.
+            federation_auth_origin (bytes|None): domain to authenticate as, for federation
         Returns:
             A tuple of (code, response)
         Raises:
@@ -226,8 +230,10 @@ class MockHttpResource(HttpServer):
         mock_request.getClientIP.return_value = "-"
 
         headers = {}
-        if federation_auth:
-            headers[b"Authorization"] = [b"X-Matrix origin=test,key=,sig="]
+        if federation_auth_origin is not None:
+            headers[b"Authorization"] = [
+                b"X-Matrix origin=%s,key=,sig=" % (federation_auth_origin, )
+            ]
         mock_request.requestHeaders.getRawHeaders = mock_getRawHeaders(headers)
 
         # return the right path if the event requires it