How to append an Authentication Header Token when POSTing data to an API in C++

A guide on how to pass an authentication token via the Authentication Header when POSTing data to an API using C++. The example utilizes the `libcurl` library to perform HTTP requests with token-based authentication.

This article explains how to use the libcurl library to perform a POST request to an API while including an Authentication Header with a token. Unlike other languages with built-in HTTP methods, C++ requires an external library like libcurl to send HTTP requests.

C++ Code

#include <iostream>
#include <curl/curl.h>

int main() {
    // Initialize CURL object
    CURL* curl;
    CURLcode res;

    // API URL
    const char* url = "https://api.example.com/data";
    // Token for authentication
    const char* authToken = "Bearer YOUR_TOKEN_HERE";

    // Data to POST
    const char* postData = "key1=value1&key2=value2";

    // Initialize CURL
    curl = curl_easy_init();

    if(curl) {
        // Set the URL
        curl_easy_setopt(curl, CURLOPT_URL, url);

        // Set the POST data
        curl_easy_setopt(curl, CURLOPT_POSTFIELDS, postData);

        // Set the Header with the token
        struct curl_slist* headers = NULL;
        headers = curl_slist_append(headers, authToken);
        curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);

        // Perform the request and get the result
        res = curl_easy_perform(curl);

        // Check for errors
        if(res != CURLE_OK) {
            std::cerr << "CURL error: " << curl_easy_strerror(res) << std::endl;
        }

        // Clean up
        curl_slist_free_all(headers);
        curl_easy_cleanup(curl);
    }
    return 0;
}

Detailed explanation:

1. #include <curl/curl.h>: The libcurl library provides functions for making HTTP requests.
2. CURL* curl; CURLcode res;: Declares a CURL object and a result code to handle the HTTP request.
3. const char* url = "https://api.example.com/data";: The URL of the API where the POST request will be sent.
4. const char* authToken = "Bearer YOUR_TOKEN_HERE";: The authentication token, which should be replaced with a valid token.
5. curl_easy_setopt(curl, CURLOPT_URL, url);: Sets the URL for the request.
6. curl_easy_setopt(curl, CURLOPT_POSTFIELDS, postData);: Sets the data to be posted.
7. curl_slist* headers = NULL; headers = curl_slist_append(headers, authToken);: Creates a list of headers and adds the authentication token.
8. curl_easy_perform(curl);: Executes the POST request.
9. curl_easy_cleanup(curl);: Cleans up the memory after the request is completed.

System requirements:

• C++ compiler (g++/clang++)
• libcurl library
• Operating system with HTTP request support (Windows, macOS, Linux)

How to install the libraries needed to run the C++ code:

• On Linux: install libcurl using the command:

  sudo apt-get install libcurl4-openssl-dev
  

• On macOS: install via Homebrew:

  brew install curl
  

• On Windows: download and install from the libcurl official website.

Tips:

• Make sure to use a valid token and keep it secure.
• Check the API response to handle errors effectively.
• For multiple requests, consider optimizing the management of CURL memory.

---