Absent or malformed "resource" parameter for /.well-known/webfinger doesn't return 400

[progval]

Expected behaviour

From RFC 7033:

4.2. Performing a WebFinger Query

A WebFinger client issues a query using the GET method to the well-
known [3] resource identified by the URI whose path component is
"/.well-known/webfinger" and whose query component MUST include the
"resource" parameter exactly once and set to the value of the URI for
which information is being sought.

If the "resource" parameter is absent or malformed, the WebFinger
resource MUST indicate that the request is bad as per Section 10.4.1
of RFC 2616 [2].

Section 10.4.1 of RFC 2616:

10.4.1 400 Bad Request

The request could not be understood by the server due to malformed
syntax. The client SHOULD NOT repeat the request without
modifications.

Actual behaviour

$ curl https://pixelfed.social/.well-known/webfinger -I | head -n 1
HTTP/2 302 
$ curl https://pixelfed.social/.well-known/webfinger\?resource\=foobar -I | head -n 1
HTTP/2 404

(btw, Mastodon always incorrectly returns 404, Pleroma correctly returns 400 on absent resource, but incorrectly returns 404 on malformed resource; and Peertube correctly returns 400 on both.)

EDIT: Mastodon just fixed it: mastodon/mastodon#13759

[progval]

thanks!