Links to Mastodon accounts on servers with different LOCAL_DOMAINs and WEB_DOMAINs don't work

[PatchMixolydic]

Describe the bug
When clicking on a Mastodon link in a user's profile, it will always go to https://$LOCAL_DOMAIN/@$USERNAME, even if WEB_DOMAIN is different.

See Mastodon's setup guide for more information about LOCAL_DOMAIN and WEB_DOMAIN

To Reproduce
Steps to reproduce the behavior:

1. Set up (or find) a Mastodon server on a subdomain, with LOCAL_DOMAIN as the domain name and WEB_DOMAIN as the subdomain. For instance, set LOCAL_DOMAIN to example.com and WEB_DOMAIN to social.example.com
2. Create an account on the Mastodon server
3. Link your new Mastodon account to your itch.io account
4. Go to your itch.io profile and click on the Mastodon link
5. Notice that you went to https://example.com/@username, not https://social.example.com/@username

Alternatively, just to confirm that this happens:

1. Go to https://social.patchmixolydic.com/@patchmixolydic
2. Confirm that my Mastodon account is @[email protected]
3. Go to https://patchmixolydic.itch.io
4. Note that the linked Mastodon account is also @[email protected]
5. Click the link to my Mastodon account
6. Notice that you went to https://patchmixolydic.com/@patchmixolydic instead of the URL in step 1

Expected behavior
I expected itch.io to use the same method as Mastodon to discover the correct URL.

Screenshots

Desktop (please complete the following information):

• OS: Arch Linux (kernel ver. 6.11.5-arch1-1)
• Browser: LibreWolf (Firefox fork)
• Version: 131.0.3-1

[dos1]

Rewriting the handle to profile URL should be done using a WebFinger lookup: https://webfinger.net/lookup/?resource=patchmixolydic%40patchmixolydic.com

This would not only fix handling Mastodon instances with separate handle domains, but also make it work with other ActivityPub implementations than Mastodon.

[leafo]

Unfortunately at this time we don't have plans to have our server making HTTP requests to random other people's servers, so if the current implementation doesn't fit your needs then I recommend moving your social link into the body of your profile where you can control the href directly.