Pass a value as parameter, which is set to a bitmask, to tell libcurl which
authentication method(s) you want it to use speaking to the remote server.
The available bits are listed below. If more than one bit is set, libcurl will
first query the site to see which authentication methods it supports and then
pick the best one you allow it to use. For some methods, this will induce an
extra network round-trip. Set the actual name and password with the
#CURLOPT_USERPWD option or with the
#CURLOPT_USERNAME and the
For authentication with a proxy, see
HTTP Basic authentication. This is the default choice, and the only method
that is in wide-spread use and supported virtually everywhere. This sends
the user name and password over the network in plain text, easily captured by
HTTP Digest authentication. Digest authentication is defined in RFC2617 and
is a more secure way to do authentication over public networks than the
regular old-fashioned Basic method.
HTTP Digest authentication with an IE flavor. Digest authentication is
defined in RFC2617 and is a more secure way to do authentication over public
networks than the regular old-fashioned Basic method. The IE flavor is simply
that libcurl will use a special "quirk" that IE is known to have used before
version 7 and that some servers require the client to use.
HTTP Bearer token authentication, used primarily in OAuth 2.0 protocol.
You can set the Bearer token to use with
HTTP Negotiate (SPNEGO) authentication. Negotiate authentication is defined
in RFC 4559 and is the most secure way to perform authentication over HTTP.
You need to build libcurl with a suitable GSS-API library or SSPI on Windows
for this to work.
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 with SSPI support.
NTLM delegating to winbind helper. Authentication is performed by a separate
binary application that is executed when needed. The name of the application
is specified at compile time but is typically /usr/bin/ntlm_auth
Note that libcurl will fork when necessary to run the winbind application and
kill it when complete, calling waitpid() to await its exit when done. On POSIX
operating systems, killing the process will cause a SIGCHLD signal to be
raised (regardless of whether
#CURLOPT_NOSIGNAL is set), which must be
handled intelligently by the application. In particular, the application must
not unconditionally call wait() in its SIGCHLD signal handler to avoid being
subject to a race condition. This behavior is subject to change in future
versions of libcurl.
This is a convenience macro that sets all bits and thus makes libcurl pick any
it finds suitable. libcurl will automatically select the one it finds most
This is a convenience macro that sets all bits except Basic and thus makes
libcurl pick any it finds suitable. libcurl will automatically select the one
it finds most secure.
This is a meta symbol. OR this value together with a single specific auth
value to force libcurl to probe for un-restricted auth and if not, only that
single auth algorithm is acceptable.