Introduction to Koa JWT

koa-jwt is a middleware for Koa, a popular Node.js framework, that facilitates JSON Web Token (JWT) authentication. It provides a simple and effective way to secure your Koa applications by ensuring that requests are authenticated.

Installation

npm install koa-jwt jsonwebtoken

Basic Usage

Here’s a simple example of how to use koa-jwt in a Koa application:

  const Koa = require('koa');
  const jwt = require('koa-jwt');
  const jsonwebtoken = require('jsonwebtoken');
  const app = new Koa();
  
  const secret = 'shared-secret';

  app.use(jwt({ secret }).unless({ path: [/^\/public/] }));

  app.use(async (ctx, next) => {
    if (ctx.url.match(/^\/public/)) {
      ctx.body = 'This is a public endpoint!';
    } else {
      ctx.body = 'Private endpoint, user authenticated!';
    }
  });

  app.listen(3000);
  console.log('Server running on port 3000');

API Endpoints and Examples

Generating a Token

Use the jsonwebtoken library to generate a token:

  const token = jsonwebtoken.sign({ user: 'username' }, secret, { expiresIn: '1h' });
  console.log(token);

Securing Routes

Protect your routes by using the koa-jwt middleware:

  app.use(jwt({ secret }).unless({ path: [/^\/public/] }));

Error Handling

Handle token verification errors in your application:

  app.use(async (ctx, next) => {
    return next().catch((err) => {
      if (err.status === 401) {
        ctx.status = 401;
        ctx.body = 'Protected resource, use Authorization header to get access\n';
      } else {
        throw err;
      }
    });
  });

Complete Application Example

  const Koa = require('koa');
  const jwt = require('koa-jwt');
  const jsonwebtoken = require('jsonwebtoken');
  const app = new Koa();

  const secret = 'shared-secret';

  app.use(jwt({ secret }).unless({ path: [/^\/public/] }));

  app.use(async (ctx, next) => {
    if (ctx.url.match(/^\/public/)) {
      ctx.body = 'This is a public endpoint!';
    } else if (ctx.url.match(/^\/login/)) {
      const token = jsonwebtoken.sign({ user: 'username' }, secret, { expiresIn: '1h' });
      ctx.body = { token };
    } else {
      ctx.body = 'Private endpoint, user authenticated!';
    }
  });

  app.listen(3000);
  console.log('Server running on port 3000');

This basic example sets up a Koa server with JWT authentication. The /public endpoint is accessible without authentication, while the other routes require a valid JWT.

Conclusion

koa-jwt is an excellent tool for adding authentication to your Koa applications. By understanding and utilizing its capabilities, you can secure your endpoints effectively and build robust Node.js applications.

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