As you build your first apps, you’ll frequently encounter the terms “authentication” and “authorization.” While these terms sound similar and are often used together (sometimes abbreviated as “auth”), they represent two distinct security processes. Understanding the difference between them is crucial for creating secure applications that protect both user data and your app’s functionality.
Authentication: Proving Who You Are
Authentication is the process of verifying who someone is.
Think of authentication as the bouncer at the club entrance checking IDs. The bouncer’s job at this stage is simple: determine if you are who you claim to be. They’re not yet deciding what you can do once inside—just whether you can enter at all.
In digital terms, authentication is how your app verifies a user’s identity. This typically happens at login, when a user provides credentials that prove they are who they claim to be.
Common Authentication Methods:
- Password-based authentication: Users provide a username/email and password
- Social login: Users authenticate through Google, Facebook, GitHub, etc.
- Biometric authentication: Fingerprint or facial recognition (common in mobile apps)
- Multi-factor authentication (MFA): Combining multiple methods, like a password plus a one-time code
- Magic links: Sending a login link to a verified email address
Authentication Examples:
- Sarah logs into your photo sharing app by entering her email and password. The system checks these credentials against what’s stored in the database. This is authentication—confirming Sarah is really Sarah.
- A banking app asks for your fingerprint before showing any account information. The app is authenticating you—verifying your identity—before proceeding.
- You sign into a new service using “Login with Google.” You’re using Google to authenticate your identity to the new service.
Authorization: Determining What You Can Do
Authorization is the process of verifying what someone is allowed to do.
Continuing our club analogy: once past the bouncer, authorization is like the VIP wristband system inside. Regular wristbands might grant access to the main floor, while VIP wristbands allow entry to exclusive areas. Your wristband authorizes what you can access within the club.
In your app, authorization happens after authentication and determines what parts of the application and what data a user can access or modify.
Common Authorization Approaches:
- Role-based access control (RBAC): Permissions based on assigned roles (admin, editor, viewer)
- Attribute-based access control (ABAC): Permissions based on user attributes and environmental factors
- Permission flags: Specific permission settings for individual actions
- Resource ownership: Access controls based on who created or owns a resource
Authorization Examples:
- Sarah has successfully logged into your photo sharing app (authentication), but she can only edit or delete her own photos, not anyone else’s. This permission check is authorization.
- In a project management tool, team members can view all projects, but only project managers can create new projects or add team members. Both project managers and team members are authenticated users, but they have different authorizations.
- An admin user in your app can access user management screens and modify system settings, while regular users cannot see these sections at all. The system is enforcing different authorizations based on user roles.
Why the Distinction Matters
Confusing authentication and authorization leads to common security mistakes:
Authentication Without Proper Authorization
Imagine building a social network where users can view profile pages at URLs like /profile/123. A new developer might check if a user is logged in (authenticated) before showing the page, but forget to verify whether the logged-in user should have access to that specific profile.
This creates an authorization vulnerability: any authenticated user could simply change the ID in the URL to access other users’ private profiles.
// BAD EXAMPLE - Authentication without authorization
function viewProfile(profileId) {
if (isUserLoggedIn()) { // Authentication check
// Missing authorization check!
return getProfileData(profileId);
} else {
return "Please log in to view profiles";
}
}
// GOOD EXAMPLE - Both authentication and authorization
function viewProfile(profileId) {
if (!isUserLoggedIn()) { // Authentication check
return "Please log in to view profiles";
}
if (canUserAccessProfile(currentUser, profileId)) { // Authorization check
return getProfileData(profileId);
} else {
return "You don't have permission to view this profile";
}
}
Authorization Checks Without Authentication
Another mistake is implementing authorization checks without ensuring proper authentication first. This happens when developers add code to check permissions but don’t verify the user’s identity.
For example, an API endpoint might check a user permission flag but not properly validate the authentication token, potentially allowing attackers to forge or manipulate requests.
Common Implementation Approaches
Authentication Implementation
Authentication typically happens at specific entry points in your application:
- Login pages
- API endpoints that issue tokens
- OAuth callback routes
Most frameworks provide authentication middleware that runs before your route handlers, ensuring a user is authenticated before proceeding further.
Authorization Implementation
Authorization usually occurs:
- Within individual route handlers or controllers
- At the database query level
- Via middleware that runs after authentication
- Through declarative rules in UI components
Many frameworks offer policy-based authorization systems that let you define rules centrally and apply them throughout your application.
Avoiding Common Auth Mistakes
- Always authenticate before authorizing. It doesn’t make sense to check what someone can do until you know who they are.
- Check authorization on every request, not just when rendering UI. An attacker might bypass your UI and make API requests directly.
- Apply authorization checks at multiple levels for sensitive operations: in the UI (to provide a good user experience), in API controllers (to protect your service), and in database queries (as a final safety net).
- Don’t rely on obscurity. Just because a button isn’t visible in the UI doesn’t mean the underlying functionality is protected.
- Use your framework’s built-in auth systems rather than rolling your own. Authentication and authorization are complex security domains with many edge cases.
Conclusion
Authentication and authorization work together to create a secure application, but they serve distinct purposes. Authentication verifies identity (who you are), while authorization controls access (what you can do).
As you build your app, think about these processes separately:
- How will users prove their identity to your system?
- Once identified, what should different users be allowed to do?
By maintaining this clear distinction, you’ll create more secure applications and avoid common security pitfalls that could expose user data or allow unauthorized actions.