Asterisk Form (*)

The asterisk is a special request-target form and registry wildcard, not a method or a literal header name.

OPTIONS * HTTP/1.1 targets the server as a whole, the fixed HTTP/2 connection preface is "PRI * HTTP/2.0", and * is a registered HTTP field-name wildcard used in values such as "Vary: *".

httpprotocolhttp2registry

Reference (http)

OPTIONS * HTTP/1.1
Host: example.com

PRI * HTTP/2.0

OPTIONS * HTTP/1.1 targets the server as a whole, the fixed HTTP/2 connection preface is "PRI * HTTP/2.0", and * is a registered HTTP field-name wildcard used in values such as "Vary: *".

Common mistakes

Sending * as a literal method or header name; it only has defined meaning as a request target and inside wildcard-aware field values.

Sources

MDN HTTP Reference