loosely based on the freebsd implementation, implement https
connection settings to override CA, and use client certificate.
new files supported in /etc/apk/:
ca.pem - if exists, it contains CAs acceptable for https
(otherwise system wide CAs are used)
crl.pem - if ca.pem is used, this is the (optional) CRL for it
cert.pem - used as client authentication certificate (+ key)
cert.key - used as client key (can be also inside cert.pem)
ftp://ftp.fu-berlin.de/unix/NetBSD/packages/current-src/pkgsrc/net/libfetch/files
libfetch comes (at least) in netbsd and freebsd flavors which
differing functionality. Alpine and Arch package netbsd one,
but it's not widely packaged across other distributions.
We need NetBSD version as it does not use funopen(3) which is not
supported in musl, and supports connection pooling.
FreeBSD seems to be the orignal and better maintained version
with support for SSL CAs, client certificate authentication,
proxy authentication, and improved http redirect handling.
So this imports NetBSD version, and future commits will pick up
the needed improvements from FreeBSD tree.
Incidentally, this also fixes#7857 and likes for good.
A. Wilcox