OAuth 2.0 (Open Authorization 2.0) - An Overview

OAuth2:

OAuth 2.0 (Open Authorization 2.0) is an industry-standard protocol for secure authorization and access delegation. It allows applications to access resources on behalf of a user without sharing their username and password.

OAuth2 is widely used for API security, enabling single sign-on (SSO), third-party logins, and secure API access.

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Key Features of OAuth 2.0:

• Token-Based Authentication – Uses access tokens instead of passwords.
• Delegated Authorization – Grants limited access to third-party apps.
• Supports Multiple Flows – Works for web apps, mobile apps, and APIs.
• Secure & Scalable – Prevents unauthorized access with scopes & expiration.
• Used by Major Platforms – Google, Facebook, Microsoft, AWS, and more.

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How OAuth 2.0 Works (Simplified Flow):

• User Requests Access → A user tries to log in to an application via Google, Facebook, etc.
• Authorization Request → The app redirects the user to an Authorization Server (e.g., Google OAuth).
• User Grants Permission → The user approves access to their data (e.g., email, contacts).
• Authorization Server Issues a Token → The app gets an Access Token (temporary key).
• Application Accesses Resources → The app uses the token to fetch user data without needing the password.

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OAuth 2.0 Grant Types (Authorization Flows)

Flow Type	Use Case	Example
Authorization Code Flow	Secure login for web apps & APIs.	Google Sign-In for websites.
Implicit Flow	Used in legacy single-page applications (SPA).	Browser-based apps.
Client Credentials Flow	Machine-to-machine authentication (M2M).	API integrations between systems.
Password Grant	Allows login with username/password (not recommended).	Internal enterprise applications.
Refresh Token	Extends access without requiring user login again.	Mobile apps keeping sessions active.

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OAuth 2.0 vs. Other Authentication Methods

Method	Authentication Type	Use Case
Basic Authentication	Username & password.	Legacy applications.
OAuth 2.0	Token-based access.	Modern web & mobile apps, API security.
API Key	Static key in headers.	Simple API access, not user specific.
SAML (Security Assertion Markup Language)	XML-based SSO authentication.	Enterprise-level authentication.

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Where is OAuth 2.0 Used?

• Social Media Login – "Sign in with Google/Facebook/LinkedIn."
• API Security – RESTful APIs in cloud & SaaS applications.
• Mobile & Web Apps – Securing third-party app access to user data.
• IoT & Machine-to-Machine (M2M) – Device authentication.