The (request-target) used by Pleroma is non-standard, but many HTTP
signature implementations do it this way due to a misinterpretation of
the draft 06 of HTTP signatures: "path" was interpreted as not having
the query, though later examples show that it must be the absolute path
with the query part of the URL as well.
This behavior is kept to make sure most software (Pleroma itself,
Mastodon, and probably others) do not break, but Pleroma now accepts
signatures for a (request-target) containing the query, as expected by
many HTTP signature libraries, and clarified in the draft 11 of HTTP
signatures.
Additionally, the new draft renamed (request-target) to @request-target.
We now support both for incoming requests' signatures.
Sean King