PawPub uses WebFinger to look up actors by their handles. The link entry uses a rel of https://pawpub.entities.org.uk/rel/actor, the type should be application/json, and the href should point to the URI of the actor being looked up.

Since handles can contain any text whatsoever, it's important to URL-encode the local part of the acct: resource before looking it up.

For example, if you wanted to resolve the handle @зима@social.example, you would send this HTTP request:

GET /.well-known/webfinger?resource=acct:%D0%B7%D0%B8%D0%BC%D0%B0@social.example HTTP/1.1
Host: social.example
Accept: application/jrd+json, application/json

to which you might receive this response:

HTTP/1.1 200 OK
Content-Type: application/jrd+json
 
{
    "subject": "acct:%D0%B7%D0%B8%D0%BC%D0%B0@social.example",
    "links": [
        {
            "rel": "https://pawpub.entities.org.uk/rel/actor",
            "href": "https://social.example/actor/12",
            "type": "application/json"
        }
    ]
}