Single Sign-On

Single Sign-On Overview

Single Sign-On is a building block you will reach for often in authentication. It keeps related logic together and makes your intent obvious to reviewers and future maintainers.

When you learn single sign-on properly, you avoid the guesswork that leads to bugs and rework. The example below shows the shape you will use in most real authentication projects.

import express from 'express';
import jwt from 'jsonwebtoken';

const app = express();
app.use(express.json());

function authenticate(req, res, next) {
  const token = req.headers.authorization?.replace('Bearer ', '');
  try {
    req.user = jwt.verify(token, process.env.JWT_SECRET);
    next();
  } catch {
    res.status(401).json({ error: 'Unauthorized' });
  }
}

Authentication middleware verifies the caller's identity before protected handlers run.

Single Sign-On Example

// verify the caller on every protected request
function authenticate(req, res, next) {
  const token = req.headers.authorization?.replace('Bearer ', '');
  req.user = verifyToken(token); // throws if invalid
  next();
}

• Start from a minimal Single Sign-On example and grow it only as needed.
• Keep configuration explicit so Single Sign-On behaves the same in every environment.
• Name things clearly so teammates understand your Single Sign-On at a glance.
• Add tests around Single Sign-On early to lock in expected behaviour.

Authentication Cheatsheet

Quick authentication reference related to single sign-on.

How Single Sign-On Works

Single Sign-On is part of proving who a user is and what they are allowed to do. Authentication verifies identity, while authorization decides access — and single sign-on plays a specific role in that flow.

Authentication middleware verifies the caller's identity before protected handlers run.

• Never store or log plain-text passwords or secrets.
• Prefer short-lived tokens with refresh over long-lived ones.
• Always send credentials over HTTPS.
• Fail closed: deny access when anything is uncertain.

Security Guidance for Single Sign-On

Security is the whole point of single sign-on. Small mistakes — weak hashing, tokens in localStorage, missing rate limits — are exactly what attackers look for, so follow proven defaults.

Common Mistakes

• Skipping error handling and edge cases when wiring up single sign-on.
• Leaving single sign-on untested, so regressions slip into production.
• Over-engineering single sign-on before you actually need the extra flexibility.
• Ignoring documentation, which makes single sign-on hard for the next developer to change.

Key Takeaways

• Single Sign-On is a core part of working effectively with authentication.
• Start small and keep single sign-on focused on a single responsibility.
• Apply consistent patterns so single sign-on scales across your project.
• Test and document single sign-on to keep it maintainable over time.