How should I edit my programm to provide succ essfull execution of my request to the privat e server

Hello everyone,
I work on Linux #astra31+ci49-Ubuntu with  GNU/Linux. 
On my system installed curl 7.68.0 (x86_64-pc-linux-gnu) libcurl/7.68.0 OpenSSL/1.1.1k zlib/1.2.11 brotli/1.0.7 libidn2/2.0.5 libpsl/0.20.2 (+libidn2/2.0.5) libssh2/1.11.0 nghttp2/1.36.0 librtmp/2.3.
From this system I can get the data from some device usung console request to the private https server via the curl command:
 
curl -k -X GET -H 'Authorization: Bearer nokey'   https://<IP-address>:<port>/api/ccu/online
 
This command requests the device-IDs, connected to this server
As a response to this command I got data in JSON-format, that represents real data from selected device:
 
["860621065932826"]
 
This number represents the device-ID of connected device.
I would like to create a programm on base of C-examples from your site, using the calls of the libcurl, which could perform the same task as the console curl command mentioned above.
 
This is the text of my C-programm, having the name curl_example.c:
 
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
 
#include <curl/curl.h>
#include <curl/easy.h>
 
static size_t write_data(void *ptr, size_t size, size_t nmemb, FILE* data)
{
  int written = fwrite(ptr, size, nmemb, data);
 
  printf("write_data: was written %i bytes into the file %s\n", written, data);
 
  return written;
}
 
int main(void)
{
  CURL *curl_handle;
    
  // Open files for the header and the body
  static const char *headerfilename = "head.txt";
  static const char *bodyfilename = "body.html";
  CURLcode Ret;
 
  FILE *header_file = fopen(headerfilename, "w");
  if (header_file == NULL)
  {
    printf("Can't open %s header_file", headerfilename);
    return -1;
  }
  
  FILE *body_file = fopen(bodyfilename, "w");
  if (body_file == NULL)
  {
    printf("Can't open %s body_file", bodyfilename);
    return -1;
  }
 
  curl_global_init(CURL_GLOBAL_ALL);
 
  /* curl session ininializatio */ 
  curl_handle = curl_easy_init();
  if (!curl_handle)
  {
    printf("Error after curl_easy_init, curl_handle=%l\n", curl_handle);
    return -1;
  }
 
  /* setup URL */ 
  Ret = curl_easy_setopt(curl_handle, CURLOPT_URL, "https://172.16.30.13:8443/api/ccu/online");
  if (Ret != CURLE_OK)
  {
     printf("Error %i after curl_easy_setopt CURLOPT_URL\n", Ret);
        curl_easy_cleanup(curl_handle);
        return -1;
  }
     
  /* set authentification */
  Ret = curl_easy_setopt(curl_handle, CURLOPT_HTTPAUTH, CURLAUTH_BEARER);
  if (Ret != CURLE_OK)
  {
    printf("Error %i after curl_easy_setopt CURLOPT_HTTPAUTH\n", Ret);
    curl_easy_cleanup(curl_handle);
    return -1;
  } 
 
  Ret = curl_easy_setopt(curl_handle, CURLOPT_XOAUTH2_BEARER, "nokey");
  if (Ret != CURLE_OK)
  {
    printf("Error %i after curl_easy_setopt CURLOPT_XOAUTH2_BEARER\n", Ret);
    curl_easy_cleanup(curl_handle);
    return -1;
  } 
 
  /* perform GET request */
  Ret = curl_easy_setopt(curl_handle, CURLOPT_HTTPGET, 1L);
  if (Ret != CURLE_OK)
  {
    printf("Error %i after curl_easy_setopt CURLOPT_HTTPGET\n", Ret);
    curl_easy_cleanup(curl_handle);
    return -1;
  } 
  
  /* no progress meter please */
  Ret = curl_easy_setopt(curl_handle, CURLOPT_NOPROGRESS, 1L);
  if (Ret != CURLE_OK)
  {
      printf("Error %i after curl_easy_setopt CURLOPT_NOPROGRESS\n", Ret);
         curl_easy_cleanup(curl_handle);
        return -1;
  }
  
  /* declare write_data as callback */
  Ret = curl_easy_setopt(curl_handle, CURLOPT_WRITEFUNCTION, write_data);
  if (Ret != CURLE_OK)
  {
    printf("Error %i after curl_easy_setopt CURLOPT_WRITEFUNCTION\n", Ret);
    curl_easy_cleanup(curl_handle);
    return -1;
  }
 
  /* save the body  */
  Ret = curl_easy_setopt(curl_handle, CURLOPT_WRITEDATA, body_file);
  if (Ret != CURLE_OK)
  {
    printf("Error %i after curl_easy_setopt CURLOPT_WRITEDATA\n", Ret);
        curl_easy_cleanup(curl_handle);
        return -1;
  }
 
  // save the header 
  Ret = curl_easy_setopt(curl_handle, CURLOPT_HEADERDATA, header_file);
  if (Ret != CURLE_OK)
  {
    printf("Error %i after curl_easy_setopt CURLOPT_HEADERDATA\n", Ret);
        curl_easy_cleanup(curl_handle);
        return -1;
  }
  
  /* get it! */
  Ret = curl_easy_perform(curl_handle);
  if (Ret != CURLE_OK)
  {
    printf("Error %i after curl_easy_perform\n", Ret);
        curl_easy_cleanup(curl_handle);
        return -1;
  }
 
  /* close the header file */
  fclose(header_file);
 
  /* close the body file */
  fclose(body_file);
 
  /* cleanup curl stuff */
  curl_easy_cleanup(curl_handle);
 
  printf("\nDone!\n");
  getchar();
  return 0;
}
 
Excuse me, that I put here whole text, becase I really don’t know, where could be a mistake.
I compiled the programm with command:
 
gcc -o curl_example curl_example.c -lcurl
 
and then started it putting as command
./curl_example
 
End, finally I got error message:
 
Error 60 after curl_easy_perform
 
Here is an explanation:
 
  CURLE_PEER_FAILED_VERIFICATION, /* 60 - peer's certificate or fingerprint  wasn't verified fine */
 
I am a novice in programing in this area. What I did incorrectly and how it should be done? 
 
Thanks in advance!
--
Vladislav Korobov
--
 
 
 
 

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