OAuth 2.0 Client Credentials Flow for Server API Access

const axios = require('axios');
// require('dotenv').config(); // Uncomment if using .env file

const OAUTH_TOKEN_URL = 'https://api.example.com/oauth/token'; // Your OAuth provider's token endpoint
const CLIENT_ID = process.env.OAUTH_CLIENT_ID || 'your_client_id';
const CLIENT_SECRET = process.env.OAUTH_CLIENT_SECRET || 'your_client_secret'; // Keep this secret!
const SCOPE = 'read write'; // Optional: specify required scopes

/**
 * Fetches an OAuth 2.0 access token using the Client Credentials Flow.
 * @returns {Promise<string>} A promise that resolves with the access token.
 */
async function getClientCredentialsAccessToken() {
  try {
    const response = await axios.post(OAUTH_TOKEN_URL, new URLSearchParams({
      grant_type: 'client_credentials',
      client_id: CLIENT_ID,
      client_secret: CLIENT_SECRET,
      scope: SCOPE,
    }).toString(), {
      headers: {
        'Content-Type': 'application/x-www-form-urlencoded',
        // Basic Authorization header can also be used:
        // 'Authorization': `Basic ${Buffer.from(`${CLIENT_ID}:${CLIENT_SECRET}`).toString('base64')}`,
      },
    });

    const accessToken = response.data.access_token;
    if (!accessToken) {
      throw new Error('Access token not found in response.');
    }
    console.log('Successfully obtained access token (first 10 chars):', accessToken.substring(0, 10) + '...');
    return accessToken;
  } catch (error) {
    console.error('Error obtaining OAuth token:', error.response ? error.response.data : error.message);
    throw new Error('Failed to get access token using client credentials.');
  }
}

// Example usage: Fetching a token and then using it for an API call
(async () => {
  try {
    const accessToken = await getClientCredentialsAccessToken();
    
    // Now use this accessToken to make authenticated API calls
    const protectedResourceUrl = 'https://api.example.com/protected/data';
    const apiResponse = await axios.get(protectedResourceUrl, {
      headers: {
        'Authorization': `Bearer ${accessToken}`,
      },
    });

    console.log('Protected API Data:', apiResponse.data);

  } catch (error) {
    console.error('Failed to perform API integration with OAuth:', error.message);
  }
})();