OAuth 2.0 and JWT Authorization in PHP: A Complete Guide for Beginners

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Introduction: Why are OAuth 2.0 and JWT needed in modern web applications?

In modern web development, secure data transfer between the client and server is one of the key tasks. Traditional authentication methods, such as cookie-based sessions, work well for monolithic applications but become inconvenient when building REST APIs, mobile applications, or microservice architectures. This is where two powerful tools come to the rescue: the OAuth 2.0 protocol and the JWT (JSON Web Token) token format.

In this article, we will break down the basic concepts of OAuth 2.0 and JWT, and then step by step create a simple authorization system in PHP. The article is aimed at beginner developers, so all explanations will be as simple as possible and accompanied by practical code examples.

What is OAuth 2.0 and how does it work?

OAuth 2.0 is an authorization protocol that allows applications to obtain limited access to user resources without transmitting their login and password. Imagine you want to log into a website using your Google or Facebook account — that is OAuth 2.0 in action.

Main roles in OAuth 2.0

Resource Owner — the user who owns the data.
Client — the application that wants to access the user's data.
Authorization Server — the server that issues tokens after successful authentication.
Resource Server — the server that stores protected data and verifies tokens.

Authorization Code Grant flow

The most common and secure OAuth 2.0 flow looks like this:

The client redirects the user to the authorization server.
The user logs in and grants permission.
The authorization server returns an authorization code to the client.
The client exchanges the code for an access token.
Using the access token, the client accesses the resource server.

What is JWT and why is it so popular?

JWT (JSON Web Token) is a compact and self-contained token format used to transmit information between parties as a JSON object. The information in a JWT can be verified and trusted because the token is digitally signed.

JWT Structure

A JWT consists of three parts separated by dots:

header.payload.signature

Header — contains the token type (JWT) and the signing algorithm (e.g., HS256 or RS256).
Payload — contains data (claims) such as the user ID, role, token creation and expiration time.
Signature — created by encrypting the header and payload using a secret key.

Advantages of JWT

Self-contained — all necessary information is stored inside the token, reducing the load on the database.
Security — the token is signed, so it cannot be tampered with.
Versatility — works with any programming language and platform.
Scalability — ideal for microservices and distributed systems.

Practical Implementation: Building an Authorization System in PHP

Now let's move on to the most interesting part — writing code. We will create a simple PHP script that generates a JWT token and verifies it with each request. To work with JWT, we will use the firebase/php-jwt library.