Add management endpoints for account validity

docs/admin_api/account_validity.rst

@@ -0,0 +1,42 @@
+Account validity API
+====================
+
+This API allows a server administrator to manage the validity of an account. To
+use it, you must enable the account validity feature (under
+``account_validity``) in Synapse's configuration.
+
+Renew account
+-------------
+
+This API extends the validity of an account by as much time as configured in the
+``period`` parameter from the ``account_validity`` configuration.
+
+The API is::
+
+    POST /_matrix/client/unstable/account_validity/send_mail
+
+with the following body:
+
+.. code:: json
+
+    {
+        "user_id": "<user ID for the account to renew>",
+        "expiration_ts": 0,
+        "enable_renewal_emails": true
+    }
+
+
+``expiration_ts`` is an optional parameter and overrides the expiration date,
+which otherwise defaults to now + validity period.
+
+``enable_renewal_emails`` is also an optional parameter and enables/disables
+sending renewal emails to the user. Defaults to true.
+
+The API returns with the new expiration date for this account, as a timestamp in
+milliseconds since epoch:
+
+.. code:: json
+
+    {
+        "expiration_ts": 0
+    }