OAuth 2.0 is the industry-standard protocol for authorisation, enabling users to grant applications access to resources (data or functionality) without sharing passwords. OAuth 2.0 powers social login, third-party integrations, and API access across the web.
OAuth 2.0 Roles
Resource Owner - the user who controls data or resources. User decides what access to grant applications.
Client Application - the application requesting access to user data, such as a web or mobile application wanting to post on user's behalf.
Authorisation Server - trusted service (Google, Facebook, GitHub) managing user authentication and issuing access tokens representing user consent.
Resource Server - service hosting protected resources (user profile data, documents). Resource servers validate access tokens before providing resources.
OAuth 2.0 Flows
Authorization Code Flow - most common OAuth flow for web applications:
- User clicks "Sign in with Google" or similar
- Application redirects user to authorisation server
- User authenticates and consents to requested permissions
- Authorisation server redirects user back with authorisation code
- Application exchanges code for access token
- Application uses access token to access user resources
Implicit Flow - simplified flow for single-page applications. Authorisation server returns access token directly rather than requiring code exchange. Less secure; being deprecated.
Resource Owner Password Credentials Flow - user provides credentials directly to application, which exchanges credentials for access token. Requires high trust; inappropriate for untrusted applications.
Client Credentials Flow - application authenticates directly with authorisation server without user involvement. Used for service-to-service authentication.
Scopes and Permissions
OAuth scopes define what access is granted. Users consent to specific scopes rather than blanket access. Scopes should be minimalist; only requesting necessary access.
Common scopes include "read-only" access or write access for specific data types. Scope definitions are provider-specific.
Access Tokens
Access tokens represent user consent and authorisation. Tokens are bearer tokens, meaning any holder can use them. Tokens should be treated as sensitive as passwords.
Token lifetime should be limited (typically 1 hour), with refresh tokens enabling obtaining new access tokens without user re-authentication.
Refresh Tokens
Refresh tokens are long-lived credentials enabling obtaining new access tokens when current tokens expire. Refresh tokens should be stored securely and sent only over HTTPS.
OAuth Security Best Practices
Use HTTPS - OAuth communications must always use HTTPS preventing interception and token theft.
Validate Redirect URIs - applications must verify that authorisation servers redirect users only to registered redirect URIs, preventing redirect attacks.
Use State Parameter - applications should include random state values in authorisation requests, verifying state in responses prevents Cross-Site Request Forgery (CSRF) attacks.
Securely Store Tokens - access tokens and refresh tokens should be stored securely:
- Web applications: secure HTTP-only cookies
- Mobile applications: secure storage (iOS Keychain, Android Keystore)
- Never store tokens in localStorage or insecure storage
Validate Tokens - resource servers must validate tokens verifying signature and expiration before granting access.
PixelForce OAuth Implementation
PixelForce's development of applications integrating with multiple platforms and services leverages OAuth for secure social login and third-party integrations. OAuth is implemented throughout our applications enabling seamless user experiences.
OpenID Connect
OpenID Connect extends OAuth 2.0 adding identity verification through ID tokens containing user identity information. OpenID Connect enables authentication whilst OAuth 2.0 provides authorisation.
PKCE (Proof Key for Code Exchange)
PKCE prevents authorisation code interception attacks in OAuth flows, particularly important for mobile and single-page applications vulnerable to code interception.
JWT Tokens
Many OAuth 2.0 implementations use JWT (JSON Web Tokens) as access token format. JWTs contain cryptographically signed user information enabling validation without token storage.
Common OAuth Vulnerabilities
Token Leakage - tokens transmitted insecurely or stored insecurely are vulnerable to theft. HTTPS and secure storage prevent leakage.
Redirect Attacks - missing or inadequate redirect URI validation enables attackers redirecting users to malicious sites capturing authorisation codes.
Token Reuse - validating state parameters and using short-lived tokens prevents attackers reusing captured codes or tokens.
Insufficient Scope Validation - applications requesting excessive permissions beyond actual requirements abuse user trust.
Revoking Access
Users should be able to revoke application access, immediately invalidating access tokens. Applications should respect revocation, re-requesting authorisation if tokens are invalidated.
Third-Party Integrations
OAuth enables safe third-party integrations. Applications integrating with third-party services should obtain explicit user consent before accessing protected resources.
Social Login Implementation
Social login using OAuth dramatically improves user experience by reducing password fatigue. Benefits include:
- Seamless account creation without email confirmation
- Pre-populated profile information
- Reduced support burden
Risks include account dependencies on social providers and potential privacy concerns.
API Access Delegation
Organisations often use OAuth to enable third-party access to user data and functionality. API providers should carefully document required scopes and grant processes.
Future OAuth Trends
Decentralised identity models and self-sovereign identity initiatives are developing alternatives to centralised OAuth providers, enabling users controlling their own identity information.
Token binding mechanisms prevent token theft even if intercepted, providing additional security layers.
Compliance Considerations
OAuth 2.0 implementations must comply with privacy regulations including GDPR and CCPA. Data sharing through OAuth should respect user consent and privacy requirements.