Account Linking

Account Linking Overview

Account Linking 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 account linking 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.

app.post('/register', async (req, res) => {
  const { email, password } = req.body;
  const existing = await db.users.findByEmail(email);
  if (existing) return res.status(409).json({ error: 'Email in use' });

  const passwordHash = await bcrypt.hash(password, 12);
  const user = await db.users.create({ email, passwordHash });
  await sendVerificationEmail(user);
  res.status(201).json({ id: user.id });
});

Registration validates input, hashes the password, and triggers email verification.

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

Authentication Cheatsheet

Quick authentication reference related to account linking.

How Account Linking Works

Account Linking is part of proving who a user is and what they are allowed to do. Authentication verifies identity, while authorization decides access — and account linking plays a specific role in that flow.

Registration validates input, hashes the password, and triggers email verification.

• 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 Account Linking

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

Common Mistakes

• Copying account linking snippets without understanding what each line does.
• Skipping error handling and edge cases when wiring up account linking.
• Leaving account linking untested, so regressions slip into production.
• Over-engineering account linking before you actually need the extra flexibility.

Key Takeaways

• Account Linking is a core part of working effectively with authentication.
• Start small and keep account linking focused on a single responsibility.
• Apply consistent patterns so account linking scales across your project.
• Test and document account linking to keep it maintainable over time.