Written by Brian Hulela
Updated at 20 Jun 2025, 17:32
3 min read
Image by Fred Moon on Unsplash
Every modern application needs a way to control access. Users need to sign in, and once inside, they should only be able to access what they’re allowed to.
This is where authentication and authorization come in. These two processes are often confused, but they serve very different roles in security. If you’re a developer, understanding how they work will help you design better, more secure applications.
Authentication is about answering one fundamental question: Who are you?
When a user logs in, the system checks their identity using one or more authentication methods:
Passwords – Simple but prone to breaches.
Biometrics – Fingerprint or facial recognition for added security.
Multi-Factor Authentication (MFA) – A second verification step, like a one-time code.
OAuth & Single Sign-On (SSO) – Logging in via Google, Apple, or another provider.
Once authentication is successful, the system knows who the user is. But that doesn’t mean they can access everything.
After authentication comes authorization, which answers the question: What can you do?
Authorization determines what actions a user is allowed to take. Some common models include:
Role-Based Access Control (RBAC) – Permissions are assigned based on roles (e.g., "admin" vs. "user").
Attribute-Based Access Control (ABAC) – Access depends on attributes like location, time, or device.
OAuth Scopes – APIs use scopes to limit what third-party apps can access.
For example, in a document editing app:
A viewer can only read the document.
An editor can make changes.
An admin can delete it.
Without proper authorization, users could access or modify things they shouldn’t.
Authentication comes first. A system can’t authorize a user if it doesn’t know who they are.
Once authenticated, authorization kicks in to control access.
A good analogy is a hotel:
Authentication is checking in at the front desk with your ID.
Authorization is your key card only unlocking your assigned room.
These two processes work together to secure applications, ensuring users can only access what they’re supposed to.
Most applications use authentication providers like Firebase Authentication, Auth0, or AWS Cognito. These services handle login, user management, and token-based authentication.
For authorization, apps often rely on:
Security Rules (like Firebase Firestore rules).
Middleware checks in backend frameworks.
Access Control Lists (ACLs) in databases.
In an API-based system, authentication is usually handled by JWTs (JSON Web Tokens). After login, a user receives a token that includes their identity. This token is sent with every request, and the backend verifies it before checking authorization.
Weak authentication can let attackers impersonate users. Poor authorization design can expose sensitive data.
As a developer, you should:
Enforce strong authentication (MFA, OAuth, secure password storage).
Follow the principle of least privilege (users should only have access to what they need).
Regularly audit access controls to prevent security risks.
Understanding authentication and authorization is fundamental to building secure applications. These concepts shape how data is protected, how users interact with systems, and how security breaches are prevented.
Next time you log in to an app, think about what’s happening behind the scenes. You’re not just entering a password—you’re proving your identity and being granted access based on predefined rules.
And that’s how secure access works.
