2 files changed, 17 insertions, 0 deletions
diff --git a/changelog.d/12133.feature b/changelog.d/12133.feature
new file mode 100644
index 0000000000..e2b194522f
--- /dev/null
+++ b/changelog.d/12133.feature
@@ -0,0 +1 @@
+Allow modules to sign JSON using the homeserver's keys.
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index a628faaf65..9504b96f8e 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -30,6 +30,7 @@ from typing import (
 
 import attr
 import jinja2
+from signedjson.sign import sign_json
 
 from twisted.internet import defer
 from twisted.web.resource import Resource
@@ -1286,6 +1287,21 @@ class ModuleApi:
         """
         await self._registration_handler.check_username(username)
 
+    def sign_json(self, body: JsonDict) -> JsonDict:
+        """Signs a dictionary with the homeserver's key, before it's sent as JSON.
+
+        Added in Synapse v1.55.0.
+
+        Args:
+            body: The dictionary to sign.
+
+        Returns:
+            The dictionary with a signature appended to it.
+            See https://github.com/matrix-org/python-signedjson#format for more
+            information on the format used.
+        """
+        return sign_json(body, self._server_name, self._hs.signing_key)
+
 
 class PublicRoomListManager:
     """Contains methods for adding to, removing from and querying whether a room