Webfinger, which the activitypub standard builds on, gives you something like this, but ultimately the provider has to actually support webfinger. This was a ne

Webfinger, which the activitypub standard builds on, gives you something like this, but ultimately the provider has to actually support webfinger. This was a neat hack though: https://github.com/bradfitz/webfist https://github.com/bradfitz/webfist But it never really went anywhere afaik.