# The conversation function

    struct pam_message {
        int msg_style;
        const char *msg;
    };

    struct pam_response {
        char *resp;
        int resp_retcode;
    };

    struct pam_conv {
        int (*conv)(int num_msg, const struct pam_message **msg,
                    struct pam_response **resp, void *appdata_ptr);
        void *appdata_ptr;
    };