Developer mode for Universal Links not bypassing Apple's CDN

Question

I'm in the process of adding a path to my apple-app-site-association file. I have made the change and have it working locally on my development machine using Ngrok as a reverse proxy. Everything has been tested and consequently I've deployed the change to my staging environment.

My staging URL is not publicly accessible as it sits behind a private network. The issue I'm facing is that despite adding ?mode=developer to my staging URL (in the entitlements file), my device does not seem to be bypassing Apple's CDN to obtain a copy of the apple-app-site-association file.

applinks:www.mydomain.com
applinks:staging.my-nonprod-domain.com?mode=developer
applinks:integration.my-nonprod-domain.com?mode=developer

I have enabled Associated Domain Development on the device and the app is being built via an active development profile.

I have had this work before, but it seems that it is not working anymore. I'm running Xcode 14.1 and iOS 16.4.1(a).

I'm out of ideas so some indication of what could be going wrong would be appreciated.

Answer 1

I came across the same thing when adding a new domain for links. Until xcode 14 there were no problems and it even worked on the simulator.

Now (Xcode 15.2) I was only able to test on the device:

1. Make sure that you have ?mode=developer in "Associated Domains" entitlements in "Signing & Capabilities" tab (or under the key com.apple.developer.associated-domains if you use plist)
2. Enable dev mode for associated domains on the phone: "Settings -> Developer -> Associated Domains Development"
3. You need to install and connect your iPhone to the proxy. Personally I use Proxyman (https://docs.proxyman.io/debug-devices/ios-device), but Charles, Fiddler and so on will work too.
4. Really important: to test universal links you need to delete the app from device. And delete it each time when you update your association json. Otherwise app wouldn't request it.
5. Run the app on your phone: in your proxy you will see list of requests to association file:

6. If you don't see direct request to your site (there was such situation in my case) — you need to block requests to the apple cdn (you can just enable ssl proxying for this domain in your proxy, then all requests will fail with ssl handshake error) and reinstall the app.

7. Optional, but handy: I tested links without existing website, so I use proxy to emulate the response from server as well. Use "map local" to the https://<your domain>/.well-known/apple-app-site-association and mock the response with the association json you want to check. Example of the json you can see on apple site (https://developer.apple.com/documentation/xcode/supporting-associated-domains)