Specify proxy URI in the form http://[USER:PASS]PROXY:PORT. USER and
PASS are optional and if they exist they must be properly
percent-encoded. This proxy is used when the backend connection is
SPDY. First, make a CONNECT request to the proxy and it connects to
the backend on behalf of shrpx. This forms tunnel. After that, shrpx
performs SSL/TLS handshake with the downstream through the tunnel. The
timeouts when connecting and making CONNECT request can be specified
by --backend-read-timeout and --backend-write-timeout options.
The -k, --insecure option is added to skip this verification. The
system wide trusted CA certificates will be loaded at startup. The
--cacert option is added to specify the trusted CA certificate file.
In client mode, now SPDY connection to the backend server is
established per thread. The frontend connections which belong to the
same thread share the SPDY connection.