Introduction to OAuth2 Server

OAuth2 is an industry-standard protocol for authorization that enables third-party applications to obtain limited access to user accounts. OAuth2 provides authorization flows for web and desktop applications, as well as mobile devices. In this article, we will explore the implementation details of an OAuth2 server, dozens of useful API endpoints with code snippets, and an example application using these APIs.

Setting Up OAuth2 Server

Before diving into the APIs, let’s set up an OAuth2 server. We’ll use Node.js with the popular library ‘oauth2-server’.

  const express = require('express');
  const OAuth2Server = require('oauth2-server');

  const app = express();
  const oauth = new OAuth2Server({
    model: require('./model'), // Model definition
    accessTokenLifetime: 3600,
    allowBearerTokensInQueryString: true,
  });

  app.use(express.json());
  app.use(express.urlencoded({ extended: false }));

  app.post('/oauth/token', (req, res, next) => {
    const request = new OAuth2Server.Request(req);
    const response = new OAuth2Server.Response(res);

    oauth
      .token(request, response)
      .then(token => {
        res.json(token);
      })
      .catch(err => {
        res.status(err.code || 500).json(err);
      });
  });

  app.listen(3000, () => {
    console.log('OAuth2 server is running on port 3000');
  });

OAuth2 API Endpoints

Obtaining an Access Token

Clients need to obtain an access token to make authorized requests to the API.

  POST /oauth/token
  Headers:
  Content-Type: application/x-www-form-urlencoded

  Body:
  grant_type=client_credentials&client_id=CLIENT_ID&client_secret=CLIENT_SECRET

Requesting Protected Resources

Access protected resources using the access token.

  GET /resource
  Headers:
  Authorization: Bearer ACCESS_TOKEN

Refreshing an Access Token

Clients can refresh the access token by providing a refresh token.

  POST /oauth/token
  Headers:
  Content-Type: application/x-www-form-urlencoded

  Body:
  grant_type=refresh_token&refresh_token=REFRESH_TOKEN&client_id=CLIENT_ID&client_secret=CLIENT_SECRET

Revoking a Token

Clients can revoke a previously issued token.

  POST /oauth/revoke
  Headers:
  Content-Type: application/x-www-form-urlencoded

  Body:
  token=TOKEN

Example Application

Here is an example of an application that uses the OAuth2 server to access protected resources.

  const axios = require('axios');

  async function authenticate() {
    const response = await axios.post('http://localhost:3000/oauth/token', {
      grant_type: 'client_credentials',
      client_id: 'CLIENT_ID',
      client_secret: 'CLIENT_SECRET'
    });

    return response.data.access_token;
  }

  async function getResource(token) {
    const response = await axios.get('http://localhost:3000/resource', {
      headers: {
        Authorization: \`Bearer \${token}\`
      }
    });

    return response.data;
  }

  async function main() {
    const token = await authenticate();
    const resource = await getResource(token);

    console.log('Protected Resource:', resource);
  }

  main().catch(console.error);

By following the steps in this guide, you can set up an OAuth2 server and implement secure API authentication in your applications.

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