Fundamental Authentication & Authorization Concepts

Building secure applications requires a solid understanding of how to properly authenticate users and control access to resources. This guide covers the essential concepts every developer should know.

Core Concepts

1. Authentication (AuthN)

Verifying who the user is - confirming a user’s identity through credentials such as username/password, biometrics, or other proof mechanisms.

2. Authorization (AuthZ)

Determining what an authenticated user can do - defining and enforcing the permissions and access rights for users within your system.

Authentication Methods

3. Session-based Auth

Stores user session on the server, tracked via cookie. The server maintains state information about the user’s logged-in status.

4. Token-based Auth

Sends tokens (like JWT) with each request instead of storing sessions server-side. This is a stateless approach to authentication.

5. JWT (JSON Web Token)

A self-contained, signed token that holds user identity and claims. JWTs are compact, URL-safe means of representing claims between two parties.

6. Access Token

Short-lived token used to access protected resources. Typically has a limited lifespan for security reasons.

7. Refresh Token

Used to obtain a new access token without re-authenticating the user. Allows for longer sessions while keeping access tokens short-lived.

8. OAuth2

A protocol for delegated access — lets third-party apps access resources without sharing credentials. Used widely for “Login with Google/Facebook” functionality.

9. OpenID Connect (OIDC)

A layer on top of OAuth2 that adds identity and login support. Extends OAuth2 with standardized user information.

10. Scopes

Define what access is being requested (e.g., read:email, write:profile). Scopes help limit what an application can do with its access token.

Access Control Models

11. RBAC (Role-Based Access Control)

Permissions granted based on user roles like admin, editor, viewer. Users are assigned roles, and roles have permissions.

12. ABAC (Attribute-Based Access Control)

Access determined by user, resource, and context attributes. More flexible than RBAC, allowing for complex access rules.

Additional Authentication Mechanisms

13. Single Sign-On (SSO)

One login grants access to multiple systems/applications. Increases convenience while reducing password fatigue.

14. 2FA / MFA

Requires an additional form of verification beyond username/password. Significantly improves security by requiring something you know and something you have.

15. Magic Links

Passwordless login method where a link is sent to the user’s email. Simple user experience with reasonable security for many use cases.

16. Social Login

Authenticate using Google, Facebook, Apple, etc. via OAuth2. Leverages existing accounts users already have.

Implementation Considerations

17. Stateful vs Stateless Auth

Stateful stores session on server; stateless relies on signed tokens like JWT. Each has performance and security tradeoffs.

18. Cookie vs LocalStorage

Cookies are sent with every request (good for sessions); localStorage is accessible via JS (use with caution). Cookies with HttpOnly flag provide better security against XSS.

19. CSRF Protection

Prevents unauthorized commands from being sent as authenticated users (especially with cookies). Defends against cross-site request forgery attacks.

20. PKCE (Proof Key for Code Exchange)

Improves OAuth security in mobile/SPAs by protecting against code interception. Essential for OAuth2 public clients.

21. Client ID & Secret

Identifiers for the application (client); secrets should never be exposed on the frontend. Keep secrets on the server side only.

22. Token Expiration & Rotation

Ensures short-lived access and renews tokens securely. Limits the damage if a token is compromised.

23. Access Denied vs Unauthenticated

“403 Forbidden” for lack of permission; “401 Unauthorized” for not being logged in. Different error responses for different situations.

24. Email Verification

Confirms email ownership before allowing access to protected features. Important for security and user account recovery.

25. Audit Logging

Tracks user actions for security and compliance purposes. Maintains a record of who did what and when.

Best Practices

• Secure Transport: Always use HTTPS for authentication requests
• Password Storage: Use proper hashing algorithms (bcrypt, Argon2) and never store plaintext passwords
• Token Handling: Keep tokens secure and use appropriate storage mechanisms
• Principle of Least Privilege: Grant only the minimum access necessary
• Regular Token Invalidation: Implement logout and token revocation mechanisms
• Rate Limiting: Protect authentication endpoints from brute force attacks

Understanding these concepts is crucial for building secure, modern applications. By implementing authentication and authorization correctly, you can protect both your users’ data and your application from various security threats.