OAuth 2.0 Client Credentials Flow for Server-to-Server Authentication

const axios = require('axios'); // or use node-fetch

async function getClientCredentialsToken(tokenUrl, clientId, clientSecret, scope = '') {
  try {
    const params = new URLSearchParams();
    params.append('grant_type', 'client_credentials');
    params.append('client_id', clientId);
    params.append('client_secret', clientSecret);
    if (scope) {
      params.append('scope', scope);
    }

    const response = await axios.post(tokenUrl, params, {
      headers: {
        'Content-Type': 'application/x-www-form-urlencoded',
      },
    });

    // The response body usually contains:
    // {
    //   "access_token": "...",
    //   "token_type": "Bearer",
    //   "expires_in": 3600,
    //   "scope": "..."
    // }
    return response.data.access_token;
  } catch (error) {
    console.error('Error obtaining client credentials token:', error.response ? error.response.data : error.message);
    throw new Error('Failed to obtain access token.');
  }
}

// Example Usage (replace with your actual values):
// const TOKEN_URL = 'https://your-oauth-provider.com/oauth/token';
// const CLIENT_ID = 'your_client_id';
// const CLIENT_SECRET = 'your_client_secret';
// const SCOPE = 'read:data write:data'; // Optional scope

// (async () => {
//   try {
//     const accessToken = await getClientCredentialsToken(TOKEN_URL, CLIENT_ID, CLIENT_SECRET, SCOPE);
//     console.log('Access Token:', accessToken);

//     // You can now use this token to make authenticated API requests
//     // const apiResponse = await axios.get('https://api.example.com/resource', {
//     //   headers: { Authorization: `Bearer ${accessToken}` }
//     // });
//     // console.log('API Response:', apiResponse.data);

//   } catch (error) {
//     console.error(error.message);
//   }
// })();