digest auth with libcurl

Hello, everyone!I want to connect to my camera using libcurl and RTSP and I've wrote simple function to do it. In case of using basic auth it works fine but I don't know how can I auth in case of digest method. Here is my code:

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <curl/curl.h>

static int
rtsp_describe(CURL *curl, const char *uri, const char *user, const char *pwd)
{   
    char *userpwd = calloc(0, strlen(user) + strlen(pwd) + 2);   
    if (userpwd == NULL) {
        fprintf(stderr, "Error: memory allocation failed!\n");
        return -1;   
    }   
    strcat(userpwd, user);   
    strcat(userpwd, ":");   
    strcat(userpwd, pwd);   
    fprintf(stdout, "RTSP: DESCRIBE %s\n", uri); 
    curl_easy_setopt(curl, CURLOPT_RTSP_STREAM_URI, uri);
    curl_easy_setopt(curl, CURLOPT_RTSP_REQUEST, CURL_RTSPREQ_DESCRIBE);   
    curl_easy_setopt(curl, CURLOPT_HTTPAUTH, CURLAUTH_DIGEST);
    curl_easy_setopt(curl, CURLOPT_USERPWD, userpwd);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, stdout);
    curl_easy_perform(curl);
    curl_easy_reset(curl);

    free(userpwd);
    return 0;
}

int
main(int argc, char **argv)
{
    if (argc != 4) {
        fprintf(stderr, "Usage: %s addr username password\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    CURLcode ret = CURLE_OK;
    const char *url = argv[1];
    char *uri = malloc(strlen(url) + 32);
    if (uri == NULL) {
        fprintf(stderr, "Error: memory allocation failed!\n");
        exit(EXIT_FAILURE);
    }

    ret = curl_global_init(CURL_GLOBAL_ALL);
    if (ret == CURLE_OK) {
        CURL *curl = curl_easy_init();
        if (curl != NULL) {
            curl_easy_setopt(curl, CURLOPT_VERBOSE, 0L);
            curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 1L);
            curl_easy_setopt(curl, CURLOPT_HEADERDATA, stdout);
            curl_easy_setopt(curl, CURLOPT_URL, url);
            snprintf(uri, strlen(url) + 32, "%s", url);
            rtsp_describe(curl, uri, argv[2], argv[3]);

            curl_easy_cleanup(curl);
        }
    }
    free(uri);
    return 0;
}

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If I delete line with CURLAUTH_DIGEST it work fine using basic auth. So, the question is, how can I login using digest auth? How can I get realm and nonce from camera in my code? Sorry, if this question is stupid, but I really stuck on it, and after my long googling I couldn't find anything useful.