CURLINFO_HTTPAUTH_AVAIL(3) on macOS

The text ec1ca7d609b5, 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.

get available HTTP authentication methods

CURLINFO_HTTPAUTH_AVAIL(3) on macOS now