Authentication & Authorization: The core differences and roles of JWT and OAuth2

In modern application development, especially in systems with user login such as web apps, mobile apps, or API backends, there are two concepts you cannot ignore: Authentication and Authorization. Although sometimes used interchangeably, the difference between them is clear and important.

And when it comes to implementing these two functions effectively, JWT (JSON Web Token) and OAuth2 are two of the most widely used technologies today.

The difference between Authentication and Authorization

Simple explanation:

• Authentication is: Who are you?
• Authorization is: What are you allowed to do?

Real-world example: When you log in to the vietswiss management system, Authentication Verify that you are a logged-in employee, and Authorization Check if you have access to the admin dashboard.

JSON Web Token (JWT): Stateless authentication

JWT is an open standard that enables secure communication between parties using structured tokens. It is particularly popular in systems RESTful API Thanks to the ability to Authentication without storing sessions on the server.

How JWT works:

1. User logs in → Server authenticates → Creates token
2. This token is sent to the client and stored (usually in localStorage or cookies).
3. Each time a client calls the API, a token is attached → The server reads and verifies the token to determine the identity.

A JWT token typically consists of three parts: header, payload, and signature – all base64-encoded, lightweight, and easy to transmit over HTTP.

⚠️ Note: JWT only encrypts, Content is not fully encrypted – Do not store sensitive information such as passwords in the payload.

OAuth2: Secure authorization between multiple systems

OAuth2 is an authorization protocol designed to allow Third parties access resources without sharing passwords. This is the technology behind the "Login with Google/Facebook" buttons you often see.

A simple example:

• You use the "Sign in with Google" button on the vietswiss page.
• Our system redirects you to Google
• After confirming the rights, Google sends back a authorization code
• vietswiss uses this code to retrieve access token and access your basic information (of course, within the limits you have permitted).

OAuth2 supports multiple flows (authorization code, implicit, password, client credentials) – suitable for different contexts such as web apps, mobile apps, or service-to-service.

When should you use JWT? When should you use OAuth2?

To choose the appropriate technology, you can refer to the following real-world scenarios:

Should use JWT When:

• You want to Building a custom authentication system without the need for third-party integration.
• Your application is internal, simple, or only a few users.
• You need an authentication solution stateful – No need to store sessions on the server.

Should use OAuth2 When:

• Your application needs to allow users to Log in with Google, Facebook, GitHub or other external services.
• Systems requiring access API on behalf of the user (e.g., reading emails from Gmail, accessing user calendars).
• Are you building Applications with multiple services (microservices) or tightly integrated with third-party systems.

👉 In practice, you can combine both: OAuth2 provides access tokens and the access token can be formatted as JWT to increase efficiency and security.

Authentication and Authorization is the foundation of any application with users.
Understand the differences and how to apply technologies such as JWT or OAuth2 will help you build a system Secure, efficient, and scalable.

At Vietswiss, we not only develop beautiful interfaces but also always focus on The security structure behind it, helping businesses operate smoothly in the digital age.