Authentication

Authentication is the process of verifying the identity of a user before allowing access to an application. It answers the question:

Who are you?

For example, when a user logs in using an email and password, the application verifies the credentials. If they are valid, the user is considered authenticated.

Why Authentication is Important

Prevents unauthorized access.
Verifies the identity of users.
Protects sensitive data and resources.
Provides a secure foundation for authorization.

Common Authentication Mechanisms

Username & Password

The most common authentication method. The user enters their credentials, which are verified by the server.

Session-Based Authentication

After a successful login, the server creates a session and stores it. The client sends a session ID (usually in a cookie) with every request. Commonly used in: Traditional web applications.

Token-Based Authentication

After login, the server generates a token. The client includes this token in every request, allowing the server to identify the user. Commonly used in: REST APIs and mobile applications.

JWT (JSON Web Token)

A widely used token-based authentication mechanism. The server issues a signed JWT after login, and the client sends it in the Authorization header for subsequent requests. Commonly used in: Modern REST APIs and microservices.

OAuth 2.0

Allows users to log in using a third-party provider without sharing their password with the application. Examples:

Single Sign-On (SSO)

A user logs in once and gains access to multiple related applications without logging in again.

Multi-Factor Authentication (MFA)

Requires more than one verification factor to authenticate a user. Examples:

Password + OTP
Password + Authenticator App
Password + Fingerprint

Authentication Flow

User Login
    │
    ▼
Verify Credentials
    │
    ▼
Authentication Successful
    │
    ▼
Issue Session or Token
    │
    ▼
Access Protected Resources

What We Will Implement

In this course, we will implement authentication using:

Password Hashing
Username & Password
JWT (JSON Web Tokens)
Protected API Endpoints
Current User Retrieval

​Authentication

​Why Authentication is Important

​Common Authentication Mechanisms

​Username & Password

​Session-Based Authentication

​Token-Based Authentication

​JWT (JSON Web Token)

​OAuth 2.0

​Single Sign-On (SSO)

​Multi-Factor Authentication (MFA)

​Authentication Flow

​What We Will Implement