pam_set_data man page
pam_set_data — set module internal data
int pam_set_data(pam_handle_t *pamh, const char *module_data_name, void *data, void (*cleanup)(pam_handle_t *pamh, void *data, int error_status));
The pam_set_data function associates a pointer to an object with the (hopefully) unique string module_data_name in the PAM context specified by the pamh argument.
PAM modules may be dynamically loadable objects. In general such files should not contain static variables. This function and its counterpart pam_get_data(3), provide a mechanism for a module to associate some data with the handle pamh. Typically a module will call the pam_set_data function to register some data under a (hopefully) unique module_data_name. The data is available for use by other modules too but not by an application. Since this functions stores only a pointer to the data, the module should not modify or free the content of it.
The function cleanup() is associated with the data and, if non-NULL, it is called when this data is over-written or following a call to pam_end(3).
The error_status argument is used to indicate to the module the sort of action it is to take in cleaning this data item. As an example, Kerberos creates a ticket file during the authentication phase, this file might be associated with a data item. When pam_end(3) is called by the module, the error_status carries the return value of the pam_authenticate(3) or other libpam function as appropriate. Based on this value the Kerberos module may choose to delete the ticket file (authentication failure) or leave it in place.
The error_status may have been logically OR'd with either of the following two values:
When a data item is being replaced (through a second call to pam_set_data) this mask is used. Otherwise, the call is assumed to be from pam_end(3).
Which indicates that the process would prefer to perform the cleanup() quietly. That is, discourages logging/messages to the user.
Memory buffer error.
Data was successful stored.
A NULL pointer was submitted as PAM handle or the function was called by an application.
pam_end(3), pam_get_data(3), pam_strerror(3)
pam(3), pam_end(3), pam_get_data(3), pam_start(3).