Subject: iOS Fails to Fetch AASA File for Internationalized Domain Names (IDN) in Unicode or Punycode Format Dear Apple Developer Relations Team And Community Members,
We are reporting a critical bug in the iOS Associated Domains feature that prevents Universal Links from working for apps using Internationalized Domain Names (IDN). Problem Description: The iOS operating system does not attempt to download the apple-app-site-association (AASA) file for domains containing non-ASCII characters (e.g., diacritics, Cyrillic). This failure occurs regardless of whether the domain is specified in the app's entitlements in its human-readable Unicode format (e.g., montréal.ca) or its encoded Punycode format (e.g., xn--montral-fya.ca, xn--e1afka0abm4b.xn--p1ai). Without fetching and validating this file, Universal Links are not activated, and the system fails to establish a connection between the website and our app. Steps to Reproduce: Create an app with the Associated Domains entitlement enabled. Add an IDN to the entitlement. We tested both formats: Format A (Unicode): applinks://montréal.ca Format B (Punycode): applinks://xn--montral-fya.ca Host a valid AASA file on our server at the correct, accessible well-known URLs for both domain representations: For montréal.ca: https://montréal.ca/.well-known/apple-app-site-association and https://xn--montral-fya.ca/.well-known/apple-app-site-association
Install the app on a device running the latest iOS version. Monitor network traffic using a tool like Charles Proxy. Observed Result: No HTTP GET request is made to any of the AASA URLs for the domains montréal.ca (in either Unicode or Punycode format) upon app installation. The system does not initiate the domain validation process. In contrast, for a standard ASCII domain (e.g., applinks://example.com), the AASA fetch is triggered immediately and is observed in the network log. Expected Result: iOS should correctly resolve the Internationalized Domain Name (whether specified in Unicode or Punycode format in the entitlement) and perform an HTTP GET request to fetch the AASA file from the /.well-known path, identical to its behavior for ASCII domains. Evidence & Configuration: Our server is configured correctly: SSL certificates are valid, the AASA file is served with the correct application/json MIME type, and is directly accessible via a browser or curl. The AASA file's syntax has been validated and is correct. The issue is reproducible on the latest versions of iOS. Impact: This bug blocks a core platform feature for millions of users in regions that use non-Latin scripts (e.g., France, Russia, China, Arab states). It makes it impossible to use Universal Links with our primary domains, severely degrading the user experience and forcing us to seek suboptimal workarounds like registering separate ASCII domains. Request: We kindly request that you investigate and log this issue as a bug in iOS and forward it to the appropriate engineering team for a fix in an upcoming update. We are prepared to provide any additional information, demo projects, or server access to assist in diagnostics. Thank you for your attention to this serious matter.
