duo - Man Page

Duo authentication service


#include <duo.h>

duo_t *
duo_open(const char *ikey, const char *skey, const char *progname, const char *cafile);

duo_set_conv_funcs(duo_t *d, char *(*conv_prompt)(void *conv_arg, const char *, char *, size_t), void (*conv_status)(void *conv_arg, const char *msg), void *conv_arg);

duo_set_host(duo_t *d, const char *hostname);

duo_set_ssl_verify(duo_t *d, int bool);

duo_login(duo_t *d, const char *username, const char *client_ip, int flags, const char *command);

const char *
duo_geterr(duo_t *d);

duo_close(duo_t *d);


The duo API provides access to the Duo two-factor authentication service.

duo_open() is used to obtain a handle to the Duo service. ikey and skey are the required integration and secret keys, respectively, for a Duo customer account. progname identifies the program to the Duo service. cafile should be NULL or the pathname of a PEM-format CA certificate to override the default.

duo_set_conv_funcs() may be used to override the internal user conversation functions. conv_prompt is called to present the user a login menu and prompt, and gather their response, returning buf or NULL on error. It may be set to NULL if automatic login is specified with DUO_FLAG_AUTO. conv_status is called to display status messages to the user, and may be NULL if no status display is needed. conv_arg is passed as the first argument to these conversation functions.

duo_set_host() may be used to override the default Duo API host.

duo_set_ssl_verify() may be used to override SSL certificate verification (enabled by default).

duo_login() performs secondary authentication via the Duo service for the specified username. client_ip is the source IP address of the connection to be authenticated, or NULL to specify the local host. The following bitmask values are defined for flags:


Attempt authentication without prompting the user, using their default out-of-band authentication factor.


Do not report incremental status during authentication (e.g. voice callback progress) - only issue one status message per authentication attempt.

If not NULL, the command to be authorized will be displayed during push authentication.

duo_geterr() returns a description of the last-seen error on the specified Duo API handle. The returned constant string should not be modified or freed by the caller.

duo_close() closes and frees the specified Duo API handle.

Return Values

duo_open() returns a pointer to the configured Duo API handle, or NULL on failure.

duo_login() returns status codes of type duo_code_t, which may have the following values:


User authenticated


User failed to authenticate


User denied by policy


Unexpected library error


Duo service unreachable


Invalid client parameters to API call


Duo service error

In the event of a DUO_*_ERROR return, duo_geterr may be called to recover a human-readable error message.

duo_geterr() returns a constant string which should not be modified or freed by the caller.

See Also

pam_duo(8), login_duo(1)


Duo Security ⟨support@duosecurity.com⟩


October 31, 2010