iOS Associated Domains (Universal Links) with Wildcards not working

Question

In an iOS app I am working on I have setup Associated Domains (Universal Links). The app hosts multiple domains. Some domains I have set up with a wildcard. These domains do not seem to work. For example, I want to link to https://news.mydomain.com/. If I add the following to the list of associated domains:

applinks:*.mydomain.com -> Does not work

applinks:news.mydomain.com -> works fine

So I believe I did set up all correct, the apple-app-site-association file is setup fine. I can even see in both cases (using Charles Proxy) the apple-app-site-association file got retrieved ok.

In the case of the wildcard, the link only opens in Safari.

When I configure the domain without a wildcard, the App opens.

Am I missing something here? I am running iOS 9.3.2 on the device and I am running Xcode 7.3.1 which are today the latest versions.

Answer 1

I added my findings to this thread: https://forums.developer.apple.com/thread/47315

In short, even in iOS 10, it appears that the wildcard setup requires that the apple-app-site-association file be served by the wildcard's root.

For instance, if you want to use *.domain.com, then the apple-app-site-association needs to be hosted at both, e.g., app1.domain.com and domain.com, else it won't work with simply specifying applinks:*.domain.com in Xcode.

This is unfortunate if your main site is hosted at www.domain.com, and that you have a 301 redirect on domain.com (which redirects you to www.domain.com), because Universal Links do not allow redirects.

The workaround I found was to create a main subdomain for your app, and to use sub-subdomains for the wildcard. E.g.

• app.domain.com (must serve the apple-app-site-association file)
• server1.app.domain.com (must serve the apple-app-site-association)
• server2.app.domain.com (...)

That way, in Xcode, you may only specify applinks:*.app.domain.com and Universal Links will work without you having to specify server1.app.domain.com, server2.app.domain.com, and so on... in Xcode.

Note, however, that you must also explicitly specify applinks:app.domain.com if you plan on using that server as well with your app.

I hope this helps.

Answer 2

It seems that adding a wildcard in the domain part of the applinks has only been introduced in iOS 9.3 Beta 2. In 9.3 Beta 2 release notes:

You can now use Universal Links with arbitrary subdomains instead of needing to list all of the app’s subdomains as fully qualified domain names. Entries have the form:

:[:port number] in which is “webcredentials”, “activitycontinuation”, or “applinks”.

The part of the entry can now optionally be prefixed with “*.” to indicate a wildcard subdomain. For example:

applinks:*.example.com

You say that you run on iOS 9.3.2. But is your deployment target >= iOS 9.3 ? If it's not: try by changing it. I think it will solve your issue.

Here you can found a copy of this release notes (sorry, I do not have any other public source)

Edit:

Even if the Apple Doc say that you can use wildcards on domains, they seems to have an issue on this:

To match all subdomains of an associated domain, you can specify a wildcard by prefixing . before the beginning of a specific domain (the period is required). Domain matching is based on the longest substring in the applinks entries. For example, if you specify the entries applinks:.mywebsite.com and applinks:*.users.mywebsite.com, matching for the domain emily.users.mywebsite.com is performed against the longer *.users.mywebsite.com entry. Note that an entry for *.mywebsite.com does not match mywebsite.com because of the period after the asterisk. To enable matching for both *.mywebsite.com and mywebsite.com, you need to provide a separate applinks entry for each.