Custom Mastodon domain using Cloudflare Workers

Use your own domain as an alias of your Mastodon handle.

When presented with a string like [email protected], Mastodon clients use the WebFinger protocol to retrieve a JSON document pointing to resources related to this account. We can make use of this by proxying requests to our own custom domain at /.well-known/webfinger to the actual Mastodon instance using Cloudflare Workers.

sequenceDiagram
  actor C as Client
  participant W as Cloudflare Worker
  participant M as Mastodon Instance

  C->>+W: GET https://pstadler.dev/.well-known/webfinger<br>?resource=acct:[email protected]
  Note over W: Find target for alias in mapping:<br>[email protected] → [email protected]
  W->>+M: GET https://infosec.exchange/.well-known/webfinger<br>?resource=acct:[email protected]
  M-->>-W: Response for [email protected]
  W-->>-C: Response for [email protected]

Configuration

Configure your aliases at the top of webfinger.js. Multiple entries are supported.

const MAPPING = new Map([
  ['[email protected]', '[email protected]'],
  ['[email protected]', '[email protected]']
])

Testing

You can test this worker locally using miniflare.

$ npm install
$ npm run dev

$ curl http://127.0.0.1:8787\?resource\=acct:[email protected]
{"subject":"acct:[email protected]","aliases":["https://infosec.exchange/@ps","https://infosec.exchange/users/ps"],"links":[{"rel":"http://webfinger.net/rel/profile-page","type":"text/html","href":"https://infosec.exchange/@ps"},{"rel":"self","type":"application/activity+json","href":"https://infosec.exchange/users/ps"},{"rel":"http://ostatus.org/schema/1.0/subscribe","template":"https://infosec.exchange/authorize_interaction?uri={uri}"}]}

Deployment

Change values in wrangler.toml according to your needs.

# Either make sure `wrangler` is available on your system, or run
# `npm install` and add `./node_modules/.bin` to your PATH variable.
$ wrangler login
$ wrangler publish

$ curl https://pstadler.dev/.well-known/webfinger\?resource\=acct:[email protected]
{"subject":"acct:[email protected]","aliases":["https://infosec.exchange/@ps","https://infosec.exchange/users/ps"],"links":[{"rel":"http://webfinger.net/rel/profile-page","type":"text/html","href":"https://infosec.exchange/@ps"},{"rel":"self","type":"application/activity+json","href":"https://infosec.exchange/users/ps"},{"rel":"http://ostatus.org/schema/1.0/subscribe","template":"https://infosec.exchange/authorize_interaction?uri={uri}"}]}

Caveats

As of early 2023, some native Mastodon clients don't seem to make use of WebFinger when searching for users, which will result in your profile not being found with this approach.