Implement stable support for MSC3882 to allow an existing device/session to generate a login token for use on a new device/session (#15388)

Implements stable support for MSC3882; this involves updating Synapse's support to
match the MSC / the spec says.

Continue to support the unstable version to allow clients to transition.

1 files changed, 28 insertions, 0 deletions

diff --git a/tests/rest/client/test_capabilities.py b/tests/rest/client/test_capabilities.py
index c16e8d43f4..cf23430f6a 100644
--- a/tests/rest/client/test_capabilities.py
+++ b/tests/rest/client/test_capabilities.py
@@ -186,3 +186,31 @@ class CapabilitiesTestCase(unittest.HomeserverTestCase):
             self.assertGreater(len(details["support"]), 0)
             for room_version in details["support"]:
                 self.assertTrue(room_version in KNOWN_ROOM_VERSIONS, str(room_version))
+
+    def test_get_get_token_login_fields_when_disabled(self) -> None:
+        """By default login via an existing session is disabled."""
+        access_token = self.get_success(
+            self.auth_handler.create_access_token_for_user_id(
+                self.user, device_id=None, valid_until_ms=None
+            )
+        )
+
+        channel = self.make_request("GET", self.url, access_token=access_token)
+        capabilities = channel.json_body["capabilities"]
+
+        self.assertEqual(channel.code, HTTPStatus.OK)
+        self.assertFalse(capabilities["m.get_login_token"]["enabled"])
+
+    @override_config({"login_via_existing_session": {"enabled": True}})
+    def test_get_get_token_login_fields_when_enabled(self) -> None:
+        access_token = self.get_success(
+            self.auth_handler.create_access_token_for_user_id(
+                self.user, device_id=None, valid_until_ms=None
+            )
+        )
+
+        channel = self.make_request("GET", self.url, access_token=access_token)
+        capabilities = channel.json_body["capabilities"]
+
+        self.assertEqual(channel.code, HTTPStatus.OK)
+        self.assertTrue(capabilities["m.get_login_token"]["enabled"])