Sign-in is the front door of your product. A weak login system can expose every customer account, so it deserves careful design. This guide explains the core parts of secure authentication in simple terms.
Never store passwords in a reversible form
Hash passwords with a modern algorithm built for this job, such as bcrypt or Argon2. Do not encrypt them, because encryption can be reversed.
Do not use a fast general-purpose hash either. This is a basic requirement.
Manage sessions carefully
- Make session tokens long, random and impossible to guess.
- Enforce session expiry on the server, not only in the browser.
- End sessions when a password changes or a user signs out.
Use multi-factor sign-in as a real second check
The second factor must be independent of the first, such as a code from a separate app or a device. Authenticator apps, passkeys (WebAuthn) and SMS are common options.
SMS has known weaknesses, and passkeys are generally the strongest option available today. Companies in the UAE working on authentication systems can see how we deliver it locally on our [custom web development in Dubai](/dubai/custom-web-development) page.
Rate limit sign-in and recovery
Sign-in, password reset and code checks are common targets for automated attacks. Limit attempts by IP address and by account on these endpoints.
We illustrate authentication systems with a documented example: see the [patient platform concept](/case-studies/healthcare). Related reading: [API Security Checklist for Modern Applications](/blog/api-security-checklist).
A short checklist for your team
- Passwords are hashed with a modern algorithm.
- Sessions expire and end on sign-out or password change.
- Sign-in and recovery endpoints are rate limited.
Secure sign-in is a set of small, correct choices: strong password storage, sensible sessions and a safe recovery flow. For help with access control in your product, read about our custom web development service.
Choose a proven hashing and session model
Store passwords with a slow, salted algorithm designed for passwords, and never in reversible form. Decide early whether the system uses server sessions or tokens, and be clear about where each one is kept. A token stored in browser local storage can be read by any script running on the page, which makes it a weaker choice for sensitive applications.
Multi-factor authentication and recovery
Offer multi-factor authentication to every user and require it for administrators. Recovery is often the weakest point.
A password reset that anyone with access to an email address can trigger undoes the strength of the login itself. Use short-lived recovery links, and notify the user whenever recovery is used.
Session lifecycle
- Expire idle sessions and cap the total lifetime of a session.
- Invalidate all sessions when a password changes.
- Rotate the session identifier after sign-in.
- Show users their active sessions, with a way to end any of them.
Test these paths the way an attacker would: reuse an old token, replay a reset link, and try to reach another user’s data with a valid session.
Sector context changes authentication systems considerably, so see how we approach [finance software](/industries/finance).
