Used as a parameter of [curl->set] and CURLOPT_HTTPAUTH to direct curl to use HTTP NTLM authentication. A proprietary protocol invented and used by Microsoft. It uses a challenge-response and hash concept similar to Digest, to prevent the password from being eavesdropped.

You need to build libcurl with either OpenSSL, GnuTLS or NSS support for this option to work, or build libcurl on Windows.