relay 1xx from backend over HTTP/2, e.g. 103 Early Hints
(if client is connected using HTTP/2)
enabled by default unless disabled in lighttpd.conf with:
server.feature-flags += ( "server.h2-discard-backend-1xx" = "enable" )
Warning: backends which send 103 Early Hints should check User-Agent
before doing so since naive clients might not handle unexpected 1xx.
Some clients may take the 1xx response as the final response, expecting
only one response. Some clients might not properly handle 100 Continue
if the client did not send Expect: 100-continue with the request.
https://tools.ietf.org/html/rfc8297#section-3 Security Considerations
An HTTP Status Code for Indicating Hints (103 Early Hints)