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

Hey there, fellow JavaScript enthusiasts! Ready to dive into the world of SSH integrations? Let's roll up our sleeves and build a robust auth flow for a public SSH integration using key-based authentication. Buckle up!

Introduction

SSH key-based authentication is like the cool kid on the block when it comes to secure remote access. It's more secure than passwords and perfect for user-facing integrations. Today, we're going to walk through building an auth flow that'll make your users feel like they've got the keys to Fort Knox (but, you know, for code).

Prerequisites

I'm assuming you're already besties with Node.js and Express.js, and you've got a basic understanding of SSH concepts. If not, no worries! Take a quick detour to brush up, and then come right back. We'll be using the ssh2 and crypto libraries, so make sure you've got those installed.

Setting up the server

First things first, let's get our Express.js server up and running:

const express = require('express');
const ssh2 = require('ssh2');

const app = express();
const sshServer = new ssh2.Server({
  hostKeys: [require('fs').readFileSync('path/to/host_key')]
});

app.listen(3000, () => console.log('Express server running on port 3000'));
sshServer.listen(2222, '127.0.0.1', () => console.log('SSH server listening on port 2222'));

Generating SSH key pairs

Now, let's generate some server-side keys. We'll use these to secure our SSH connections:

const crypto = require('crypto');

function generateKeyPair() {
  return crypto.generateKeyPairSync('rsa', {
    modulusLength: 4096,
    publicKeyEncoding: { type: 'spki', format: 'pem' },
    privateKeyEncoding: { type: 'pkcs8', format: 'pem' }
  });
}

const { publicKey, privateKey } = generateKeyPair();
// Store these securely, you'll need them later!

User registration flow

When a user wants to register, they'll send us their public key. Let's set up an endpoint to handle that:

app.post('/register', (req, res) => {
  const { username, publicKey } = req.body;
  
  if (isValidPublicKey(publicKey)) {
    storeUserPublicKey(username, publicKey);
    res.status(201).send('User registered successfully');
  } else {
    res.status(400).send('Invalid public key');
  }
});

function isValidPublicKey(key) {
  // Implement your validation logic here
}

function storeUserPublicKey(username, key) {
  // Store the key securely, perhaps in a database
}

Authentication flow

Now for the main event - authenticating SSH connections:

sshServer.on('connection', (client, info) => {
  console.log('New client connected!');

  client.on('authentication', (ctx) => {
    if (ctx.method === 'publickey') {
      verifyUserPublicKey(ctx.username, ctx.key, (err, valid) => {
        if (valid) {
          ctx.accept();
        } else {
          ctx.reject();
        }
      });
    } else {
      ctx.reject();
    }
  });
});

function verifyUserPublicKey(username, key, callback) {
  // Implement your verification logic here
}

Authorization process

Once a user is authenticated, we need to decide what they're allowed to do:

client.on('session', (accept, reject) => {
  const session = accept();
  session.on('exec', (accept, reject, info) => {
    if (isAuthorized(info.username, info.command)) {
      // Execute the command
    } else {
      reject();
    }
  });
});

function isAuthorized(username, command) {
  // Implement your authorization logic here
}

Handling SSH sessions

Keep those sessions in check:

const activeSessions = new Map();

client.on('ready', () => {
  const sessionId = generateSessionId();
  activeSessions.set(sessionId, { client, lastActivity: Date.now() });
  
  // Set up a timer to check for inactive sessions
  setInterval(() => {
    const now = Date.now();
    activeSessions.forEach((session, id) => {
      if (now - session.lastActivity > SESSION_TIMEOUT) {
        session.client.end();
        activeSessions.delete(id);
      }
    });
  }, 60000); // Check every minute
});

Security considerations

Remember, with great power comes great responsibility. Rotate those keys regularly and keep an eye out for any suspicious activity. Consider implementing key expiration and don't forget to protect against common SSH attacks like brute-force attempts.

Testing the integration

Last but not least, test, test, and test again! Write unit tests for your auth flow and integration tests for SSH connections. Your future self (and your users) will thank you.

const { expect } = require('chai');
const ssh2 = require('ssh2');

describe('SSH Authentication', () => {
  it('should authenticate with valid key', (done) => {
    const conn = new ssh2.Client();
    conn.on('ready', () => {
      expect(true).to.be.true;
      conn.end();
      done();
    }).connect({
      host: '127.0.0.1',
      port: 2222,
      username: 'testuser',
      privateKey: require('fs').readFileSync('path/to/private_key')
    });
  });
});

Conclusion

And there you have it, folks! You've just built a rock-solid auth flow for a public SSH integration. Remember, this is just the beginning. There's always room for improvement, so keep exploring and refining your implementation.

Now go forth and SSH with confidence! Happy coding! 🚀