push_notifs: Require ios_app_id on register at bouncer, too.

We'll need this information in order to properly direct APNs
notifications.  Happily, the Zulip server always sends it when
registering an APNs token; and it appears it always has done so
since the commit:

cddee49e7 Add support infrastructure for push notification bouncer service.

back in 2016.  So there's no compatibility issue from requiring it.

api_docs/changelog.md

@@ -27,6 +27,12 @@ format used by the Zulip server that they are interacting with.
   Previously it defaulted to the server setting `ZULIP_IOS_APP_ID`,
   defaulting to "org.zulip.Zulip".
 
+* `POST /remotes/server/register`: The `ios_app_id` parameter is now
+  required when `kind` is 1, i.e. when registering an APNs token.
+  Previously it was ignored, and the push bouncer effectively
+  assumed its value was the server setting `APNS_TOPIC`,
+  defaulting to "org.zulip.Zulip".
+
 **Feature level 222**
 
 * [`GET /events`](/api/get-events): When a user is deactivated or

zerver/tests/test_push_notifications.py

@@ -500,6 +500,31 @@ class PushBouncerNotificationTest(BouncerTestCase):
             401,
         )
 
+    def test_register_require_ios_app_id(self) -> None:
+        endpoint = "/api/v1/remotes/push/register"
+        args = {"user_id": 11, "token": "1122"}
+
+        result = self.uuid_post(
+            self.server_uuid,
+            endpoint,
+            {**args, "token_kind": PushDeviceToken.APNS},
+        )
+        self.assert_json_error(result, "Missing ios_app_id")
+
+        result = self.uuid_post(
+            self.server_uuid,
+            endpoint,
+            {**args, "token_kind": PushDeviceToken.APNS, "ios_app_id": "example.app"},
+        )
+        self.assert_json_success(result)
+
+        result = self.uuid_post(
+            self.server_uuid,
+            endpoint,
+            {**args, "token_kind": PushDeviceToken.GCM},
+        )
+        self.assert_json_success(result)
+
     def test_register_device_deduplication(self) -> None:
         hamlet = self.example_user("hamlet")
         token = "111222"

zilencer/views.py

@@ -165,6 +165,8 @@ def register_remote_push_device(
     ios_app_id: Optional[str] = REQ(default=None),
 ) -> HttpResponse:
     validate_bouncer_token_request(token, token_kind)
+    if token_kind == RemotePushDeviceToken.APNS and ios_app_id is None:
+        raise JsonableError(_("Missing ios_app_id"))
 
     if user_id is None and user_uuid is None:
         raise JsonableError(_("Missing user_id or user_uuid"))