CURLOPT_PROXYAUTH(3) on macOS

The text 99d9ad89ca98, as macOS 10.12.5, macOS 10.12.4, macOS 10.12.3, macOS 10.12.2, macOS 10.12.1, macOS 10.12 shipped it.

set HTTP proxy authentication methods to try

CURLOPT_PROXYAUTH(3) on macOS now