LIBRESSL_LEGACY_API is drop-in replacement for LIBRESSL_IN_USE.  In
the upcoming commits, we will add changes to support libressl 2.7.

NPN has been superseeded by ALPN. OpenSSL provides a configure
option to disable npn (no-npn) which results in an OpenSSL
installation that defines OPENSSL_NO_NEXTPROTONEG in opensslconf.h

The #ifdef's look safe here (as the next_proto is initialized as
nullptr). Alteratively, macros could be defined for the used npn
methods that return a 0 for next_proto.
Signed-off-by: Bernard Spil <brnrd@FreeBSD.org>

cmake: add ENABLE_STATIC_LIB option to build static lib

Fix typo

When using the ENABLE_LIB_ONLY option, only the shared
library was built. This new option allows to build the
static library as well.

Add nghttp2_session_set_user_data() public API function

src: Define nghttp2_inet_pton wrapper to avoid inet_pton macro

nghttpx: Add an option to accept expired client certificate

nghttpx: Add mruby tls_client_not_before, and tls_client_not_after

The bug is the same bug fixed by
6deee203, but in response handler.

Fix #1119: Overwrite of first header on mruby call to env.req.set_header(..)

nghttpx: Add upgrade-scheme parameter to backend option

If "upgrade-scheme" parameter is present in backend option along with
"tls" paramter, HTTP/2 :scheme pseudo header field is changed to
"https" from "http" when forwarding a request to this particular
backend.  This is a workaround for a server which requests "https"
scheme on HTTP/2 connection encrypted by TLS.