Mastodon on your own domain without hosting a server

Like many in the past week, I have been having a serious look at Mastodon as an alternative to Twitter.

Mastodon is a social network that is distributed across many servers that have their own smaller communities, and federate with other servers to provide a more “global” social network.

There are many servers out there that you can choose from. Alternatively, you can also self-host your Mastodon server, or use one of many hosted instances, “Mastodon as a service”.

In recent hours, I have seen many people wanting to host their own servers, which is great fun! Self-hosting also has the added benefit of being able to have a Mastodon account on your own domain, and you own your data.

Now, I don’t really care about that (yet?). I ran my own mail server back in the day and am very happy with someone running it for me now. The same goes with Mastodon: I trust the folks at Mastodon.online, the server I joined, to do a much better job at this than I will ever do.

However, there is one thing I would like my own server for: discoverability. Much like with e-mail, I want folks to have an easy address to find me, and one that I can keep giving out to everyone even if later I switch to a different Mastodon server. A bit like e-mail forwarding to your ISP’s e-mail service.

The good news is: you can use your own domain and share it with other folks. It will link to your actual account.

Go on, try it. Search for @maarten@balliauw.be, and you will find my @maartenballiauw@mastodon.social.

How to discover Mastodon account via custom domain

Reading “how to implement a basic ActivityPub server”, there are a couple of things that stand out:

• Mastodon (and others) use ActivityPub as their protocol to communicate between “actors”.
• Actors are discovered using WebFinger, a way to attach information to an email address, or other online resource.

Since discovery is what I was after, WebFinger seemed like the only thing I would need to implement.

WebFinger lives on /.well-known/webfinger on a server. For Mastodon, your server will be queried for accounts using an endpoint that looks like this:

GET /.well-known/webfinger?resource=acct:accountname@server

And indeed, if I look at my Mastodon server’s webfinger for my account, I get a response back!

GET https://mastodon.online/.well-known/webfinger?resource=acct:maartenballiauw@mastodon.online

{
  "subject": "acct:maartenballiauw@mastodon.online",
  "aliases": [
    "https://mastodon.online/@maartenballiauw",
    "https://mastodon.online/users/maartenballiauw"
  ],
  "links": [
    {
      "rel": "http://webfinger.net/rel/profile-page",
      "type": "text/html",
      "href": "https://mastodon.online/@maartenballiauw"
    },
    {
      "rel": "self",
      "type": "application/activity+json",
      "href": "https://mastodon.online/users/maartenballiauw"
    },
    {
      "rel": "http://ostatus.org/schema/1.0/subscribe",
      "template": "https://mastodon.online/authorize_interaction?uri={uri}"
    }
  ]
}

Sweet!

The next thing I tried was simply copy-pasting this JSON output to my own server under .well-known/webfinger, and things magically started working.

In other words, if you want to be discovered on Mastodon using your own domain, you can do so by copying the contents of https://<your mastodon server>/.well-known/webfinger?resource=acct:<your account>@<your mastodon server> to https://<your domain>/.well-known/webfinger.

One caveat: this approach works much like a catch-all e-mail address. @anything@yourdomain.com will match, unless you add a bit more scripting to only show a result for resources you want to be discoverable.

Bonus: Discovering folks from Twitter

Discoverability, at this stage, is one of the things that matter to get a proper social graph going. Over the past days, there were a couple of tools I found very useful in finding Twitter folks on Mastodon:

• Twitodon learns about which Twitter account matches a Mastodon account, from folks using this service.
• Fedifinder and Debirdify scan Twitter accounts and checks if there is a Mastodon account in their profile data.

Good luck! And give @maarten@balliauw.be a follow if you make the jump to Mastodon.

Edit: Seems there is a GitHub issue which requests custom domains as well.