What is the Difference Between SSO and OAuth2? Understand It All in One Article!

When dealing with authentication and authorization in modern applications, terms like SSO (Single Sign-On) and *
OAuth2* frequently pop up. While both are essential components in securing and simplifying user interactions, they
serve different purposes. This article will break down the differences, their roles, and how they complement each other.
We’ll also provide examples and code snippets for a hands-on understanding.

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What is SSO?

Definition

Single Sign-On (SSO) is an authentication method that allows users to log in once and access multiple applications
or systems without needing to authenticate again. It improves user experience by eliminating repeated logins.

Key Features of SSO

• Convenience: One login for multiple services.
• Centralized Authentication: All login requests are handled by a single identity provider (IdP).
• Reduced Password Fatigue: Users don’t have to remember multiple credentials.

Common SSO Use Cases

• Enterprise environments where employees use multiple tools like Slack, Google Workspace, and Salesforce.
• Consumer platforms like Google’s ecosystem (Gmail, YouTube, Google Drive).

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What is OAuth2?

Definition

OAuth2 (Open Authorization 2.0) is a protocol for authorization, allowing a user to grant a third-party application
limited access to their resources without exposing their credentials. OAuth2 is commonly used in APIs and services.

Key Features of OAuth2

• Authorization Delegation: Users grant permissions to applications without sharing their passwords.
• Token-Based: Uses access tokens for resource access.
• Granular Permissions: Applications can request specific levels of access (e.g., read-only, write).

Common OAuth2 Use Cases

• Third-party logins (e.g., “Sign in with Google”).
• Accessing APIs (e.g., GitHub API, Twitter API).

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Key Differences Between SSO and OAuth2

Feature	SSO	OAuth2
Purpose	Centralized user authentication for multiple apps.	Delegated authorization for accessing resources.
Authentication	Yes	No (handles authorization, not authentication).
Protocol	Typically uses SAML, OpenID Connect, or Kerberos.	OAuth2 protocol.
Primary Audience	Enterprises and large-scale platforms.	API developers and service providers.
Example	Log in once to access Gmail, YouTube, and Drive.	Grant Spotify access to your Google Calendar.

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How SSO and OAuth2 Work Together

SSO and OAuth2 often complement each other. For example, SSO with OAuth2 can be implemented using OpenID Connect (
OIDC), a protocol built on top of OAuth2. OIDC adds authentication capabilities to OAuth2, enabling SSO functionality
for applications.

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Practical Example: OAuth2 Integration

Here’s a basic example of implementing OAuth2 in Node.js using Google as an OAuth2 provider.

Step 1: Set Up Your Google OAuth2 App

1. Go to the Google Cloud Console.
2. Create a new project.
3. Navigate to APIs & Services > Credentials and create an OAuth2 client ID.
4. Set the Authorized Redirect URIs (e.g., http://localhost:3000/callback).

Step 2: Install Required Dependencies

npm install express passport passport-google-oauth20

Step 3: Configure OAuth2 with Passport.js

javascriptCopy codeconst express = require('express');
const passport = require('passport');
const GoogleStrategy = require('passport-google-oauth20').Strategy;

const app = express();

// Configure Passport
passport.use(new GoogleStrategy({
  clientID: 'YOUR_GOOGLE_CLIENT_ID',
  clientSecret: 'YOUR_GOOGLE_CLIENT_SECRET',
  callbackURL: 'http://localhost:3000/callback',
}, (accessToken, refreshToken, profile, done) => {
  return done(null, profile);
}));

passport.serializeUser((user, done) => done(null, user));
passport.deserializeUser((obj, done) => done(null, obj));

app.use(passport.initialize());

// Routes
app.get('/auth/google', passport.authenticate('google', {
  scope: ['profile', 'email'],
}));

app.get('/callback', passport.authenticate('google', { failureRedirect: '/' }), (req, res) => {
  res.send('Authentication successful');
});

// Start server
app.listen(3000, () => console.log('Server running on http://localhost:3000'));

Step 4: Test the Integration

1. Start your server:
2. Visit http://localhost:3000/auth/google to begin the OAuth2 flow.
3. Log in with your Google account and authorize the application.

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Conclusion

Both SSO and OAuth2 are powerful tools in the authentication and authorization landscape. While SSO focuses on
simplifying user authentication across multiple applications, OAuth2 empowers applications to access resources securely.
Understanding their roles and differences can help you design more robust and user-friendly systems.
Try implementing OAuth2 or SSO in your application and see the benefits firsthand. Let us know your experience in the
comments!