Authentication and Authorization are two fundamental security concepts in ASP.NET Core and most modern applications.

Many interviewers ask this question together.

Quick Interview Answer

• Authentication → Who are you? 🔐

• Authorization → What can you access? 🛡️

1. Authentication (Who are you?)

Authentication is the process of verifying the user's identity.

Example:

• Username & Password

• OTP

• Fingerprint

• Login with Google

When you log in to a website:

Enter username + password

System checks:

Is this user valid?

If yes → User is Authenticated ✅

Example

Login to Gmail
Username: sampath@gmail.com
Password: *****

System verifies → You are authenticated

2. Authorization (What can you access?)

After authentication, system checks what user is allowed to do.

Example:

User	Access
Admin	Create users
HR	Add candidates
Employee	View profile

This is Authorization.

Real Example

Suppose your ATS application (hiringbegins.com from your previous project):

User logs in:

Step 1 → Authentication

Is this user valid?

Step 2 → Authorization

Is user HR or Admin?

Then show features accordingly.

Example in Code (.NET Core)

Authentication

app.UseAuthentication();

Authorization

app.UseAuthorization();

Order matters 

app.UseAuthentication();
app.UseAuthorization();

Visual Flow

User Login
    ↓
Authentication (Who are you?)
    ↓
Authorization (What can you access?)
    ↓
Access Granted

Real World Example

Bank ATM 💳

Authentication:

Insert card + PIN

Authorization:

Check account balance? ✅
Withdraw money? ✅
Close account? ❌

Interview Comparison Table 

Feature	Authentication	Authorization
Purpose	Verify identity	Check permissions
Happens first	✅ Yes	❌ No
Example	Login	Role-based access
Data used	Username/password	Roles/claims

Common Authentication Methods

• Cookies

• JWT Token

• OAuth

• OpenID Connect

Examples:

• JWT

• OAuth 2.0

• OpenID Connect

Interview One-Line Answer 

Authentication verifies who the user is, while authorization determines what the user is allowed to access.