How to build a public SSH (password-based auth) integration: Building the Auth Flow

Aug 7, 2024 • 6 minute read

Hey there, fellow JavaScript devs! Ready to dive into the world of SSH integrations? Let's build a robust auth flow for a user-facing SSH integration with password-based authentication. Buckle up, because we're about to make security both fun and functional!

Setting the Stage

First things first, let's get our environment ready. You'll need the ssh2 library, so go ahead and install it:

npm install ssh2

Create a basic project structure with client.js and server.js files. We'll flesh these out as we go along.

The Auth Flow: A Bird's Eye View

Our auth flow is going to be straightforward but secure. Here's the gist:

Client initiates connection
Server prompts for credentials
Client sends credentials
Server verifies and grants/denies access

Simple, right? Let's make it happen!

Client-Side Magic

In your client.js, let's create an SSH client:

const { Client } = require('ssh2');

const conn = new Client();

conn.on('ready', () => {
  console.log('Connection established!');
  // Do your thing here
}).connect({
  host: 'localhost',
  port: 22,
  username: 'your_username',
  password: 'your_password'
});

Pro tip: In a real-world scenario, you'd want to handle user input securely. Consider using a library like prompt for this.

Server-Side Sorcery

Now, let's set up our SSH server in server.js:

const { Server } = require('ssh2');

new Server({
  hostKeys: [/* your host keys here */]
}, (client) => {
  console.log('Client connected!');

  client.on('authentication', (ctx) => {
    if (ctx.method === 'password' && ctx.username === 'valid_user' && ctx.password === 'valid_password') {
      ctx.accept();
    } else {
      ctx.reject();
    }
  });

  client.on('ready', () => {
    console.log('Client authenticated!');
  });
}).listen(22);

Remember, hardcoding credentials is a big no-no in production. We're just keeping it simple for now!

The Heart of Authentication

The real magic happens in the authentication event handler. This is where you'll verify credentials, manage auth states, and handle failures. Let's beef it up a bit:

let attempts = 0;

client.on('authentication', (ctx) => {
  if (ctx.method === 'password') {
    attempts++;
    if (attempts > 3) {
      ctx.reject(['Too many attempts']);
      return;
    }
    
    // Here's where you'd typically check against a database
    if (ctx.username === 'valid_user' && ctx.password === 'valid_password') {
      ctx.accept();
    } else {
      ctx.reject(['Invalid username or password']);
    }
  } else {
    ctx.reject(['Only password auth is supported']);
  }
});

Securing the Fort

Security isn't just about passwords. Consider implementing rate limiting to prevent brute-force attacks. Here's a simple example:

const { RateLimiter } = require('limiter');

const limiter = new RateLimiter({ tokensPerInterval: 5, interval: 'hour' });

client.on('authentication', async (ctx) => {
  if (!(await limiter.removeTokens(1))) {
    ctx.reject(['Rate limit exceeded']);
    return;
  }
  // Rest of your auth logic here
});

Testing, Testing, 1-2-3

Don't forget to test your integration thoroughly! Write unit tests for individual components and integration tests for the entire flow. Here's a quick example using Jest:

test('authentication succeeds with valid credentials', async () => {
  const client = new Client();
  await client.connect({
    host: 'localhost',
    port: 22,
    username: 'valid_user',
    password: 'valid_password'
  });
  expect(client.authenticated).toBe(true);
});

Wrapping Up

And there you have it! You've just built a secure auth flow for a public SSH integration. Remember, this is just the beginning. In a production environment, you'd want to add proper error handling, logging, and perhaps even multi-factor authentication.

Keep exploring, keep securing, and most importantly, keep coding! SSH you later! 😉