If you've been building Spring Boot apps with basic form logins, you've probably hit the point where you need something better.

Maybe your company uses Okta, Azure AD, or some other identity provider. Maybe you want to stop managing passwords altogether. That's where OAuth2 authentication comes in.

Spring Boot OAuth2 authentication is an enterprise-grade authentication mechanism that delegates credential management to trusted identity providers. This comprehensive guide walks through implementing OAuth2 in a Spring Boot application with role-based access control, so you can restrict pages to specific users.

If you're new to Spring Security, check out our guide on custom authentication strategies first-it covers the basics before you tackle OAuth2.

This guide covers implementing OAuth2 in a Spring Boot application, including role-based access control so you can restrict pages to specific users. If you need enterprise-level authentication and are considering other approaches, SAML authentication is another solid option worth knowing about.

What is OAuth2 authentication?

OAuth2 authentication is an open standard authorization protocol that allows users to grant third-party applications access to their resources without sharing passwords. In the context of Spring Boot applications, OAuth2 enables Single Sign-On (SSO) by delegating user authentication to an external identity provider.

Simply put: instead of your application storing and validating passwords, OAuth2 authentication in Spring Boot lets an external provider (like Okta or Azure AD) handle login. Your app receives a secure token that confirms the user's identity.

OAuth2 gets talked about a lot, and honestly, it's simpler than people make it sound. At its core, you're outsourcing authentication to a third party. Your users log in somewhere else (like Okta or Google), get a token, and then that token tells your app who they are and what they can do.

If you're coming from a homegrown authentication system or the approach covered in custom authentication implementations, OAuth2 represents a significant shift-you're trusting an external provider instead of managing credentials yourself.

How does OAuth 2.0 work?

OAuth 2.0 operates through a series of steps called the OAuth2 authorization flow. Here's how Spring Boot OAuth2 authentication works in practice:

1. User initiates login: The user clicks "Log in" on your Spring Boot application.
2. Redirect to identity provider: Your app redirects them to your configured identity provider (authorization server).
3. User authenticates: The user enters their credentials at the identity provider, not your app.
4. Authorization grant: The identity provider gives your app an authorization code.
5. Token exchange: Your Spring Boot backend exchanges this code for an access token (and optionally a refresh token).
6. Access granted: Your app uses the access token to identify the user and verify their roles.
7. User logged in: The user gains access to your application's protected resources.

Key players in OAuth 2.0

• Resource owner: The person trying to log in.
• Authorization server: The system that verifies their identity (Okta, Azure AD, Google, etc.).
• OAuth2 client: Your Spring Boot application.
• Resource server: Any APIs you want to protect using the access token.

The beauty of this token-based authentication setup is you never touch passwords. The user logs in once at their identity provider, gets a token, and uses that everywhere.

OAuth2 implementation in Spring Boot: Step-by-step

Step 1: Add the dependency

If you're using Maven, add this to pom.xml:

For Gradle users, add this to build.gradle:

That's it. Spring Boot handles most of the heavy lifting for you.

Step 2: Configure Spring security

Create a SecurityConfig class. This is where you tell Spring how authentication should work. Enable method-level security too-you'll need it for role checks.

Note on HTTPS: If you're testing locally on localhost, the HTTPS requirement will cause connection errors. Comment out the .requiresChannel() block while developing, but keep it in production.

Step 3: Configure your identity provider

Tell Spring where your identity provider is and provide the credentials. Add this to application.yml. Here's an example using Okta:

Replace issuer-uri, client-id, and client-secret with values from your identity provider. The redirect-uri is where your app receives the token after login-Spring handles this automatically, no controller needed.

The openid scope is required. Without it, Spring won't get the ID token needed to extract user details.

Step 4: Map OAuth2 roles with Spring security

Here's the tricky part of Spring Security implementation steps. Your identity provider probably sends user groups or roles in the token, but Spring Security expects them in a specific format: with a ROLE_ prefix. This is where role-based access control truly comes into play.

Add this to your SecurityConfig:

This interceptor runs during login and transforms your provider's groups into Spring roles. Make sure your identity provider is configured to include groups in the ID token. In Okta, you'll need to add a custom claim called groups in your Authorization Server settings.

Step 5: Test it out

Write a simple controller to verify everything works:

Run the app. When you hit a protected endpoint, you'll be redirected to your identity provider's login page. After login, you'll be back in your app with a token and whatever roles your provider sent.