CURLOPT_TLSAUTH_USERNAME(3) on macOS

The text f3a4ef3db0a9, 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.

user name to use for TLS authentication

CURLOPT_TLSAUTH_USERNAME(3) on macOS now