How do you implement authentication and authorization in Express.js?

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In Express.js, authentication and authorization are essential for securing applications but serve different purposes:

• Authentication verifies who a user is.

• Authorization checks what the authenticated user is allowed to do.

1. Authentication

This step ensures the user’s identity. Common approaches include:

• Username/Password: Validate credentials against a database (often hashed with bcrypt).

• Sessions & Cookies: After login, create a session on the server and store a session ID in a cookie for tracking. Libraries like express-session help manage this.

• Token-Based (JWT): On successful login, generate a JSON Web Token signed with a secret. The client stores it (usually in localStorage or cookies) and sends it in the Authorization header with each request. The server verifies the token for subsequent requests.

2. Authorization

Once authenticated, define what resources the user can access:

• Role-Based Access Control (RBAC): Assign roles like admin, editor, user, and check permissions before serving a route.

• Route Protection: Middleware checks if the request has a valid session or token. If valid, it allows access; otherwise, it returns an error (e.g., 401 Unauthorized or 403 Forbidden).

• Granular Permissions: Beyond roles, you can check fine-grained rules (e.g., a user can only edit their own posts).

3. Implementation Workflow

1. User logs in → credentials verified.

2. Server issues a session or JWT.

3. Middleware checks authentication for protected routes.

4. Authorization middleware ensures user roles/permissions match the action.

👉 Example: A blog app where authentication ensures a user is logged in, and authorization ensures only the author or an admin can delete a post.

Read More :

Explain the difference between synchronous and asynchronous code in Express.

How do you secure an Express.js application?

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