Mastodon works like that: there are four custom fields. If they happen to contain an URL, they become links with rel="me", and when you save the profile those sites are contacted. If they link back to your profile, also with rel="me", they turn green with a checkmark. Best system I've seen so far.
That is what their info says. I have attempted to get it to work repeatedly. I have a couple of websites on a hosting service. I put references to them in the custom fields. I put the rel="me" line in the index page, copied exactly from the message on the Mastodon instance in the "edit profile" dialogue. Nothing happens. It does not turn the link green; it does not add "verified" to my ID. I have done this with 2 different Mastodon accounts on different instances, and with several of my websites. The Mastodon admin had no answers. Just suggested moving the code around in my index page to see if that helped. On one occasion a message flashed on the screen saying something like ""Can't verify CSRF token" It flashed and disappeared. I don't know whether that would be an issue on Mastodon or on my server. Since the verification works for other users with other websites, I suspect it is something lacking in my sites, but I have no idea what.