OAuth 2.0 Security Review: How to Protect Against Common Attacks
OAuth 2.0 is everywhere. It powers authentication for APIs, mobile apps, cloud services, and enterprise portals. It’s also one of the most targeted attack surfaces. A proper OAuth 2.0 security review is not optional. It’s the barrier between your data and the attackers who automate their probes at scale.
At its core, OAuth 2.0 is an authorization framework. It delegates access without sharing passwords. But the flexibility that makes it powerful also makes it dangerous when implemented carelessly. Misconfigurations, missing validations, and weak token handling turn a secure design into a breach vector. The most common risks surface in predictable places:
1. Redirect URI validation
Always enforce exact matching for redirect URIs. Wildcards or loose matching allow attackers to steal authorization codes by injecting malicious endpoints. Permit only whitelisted URIs, and enforce them server-side.
2. State parameter protection
Use the state parameter to defend against CSRF attacks. Generate cryptographically strong values, bind them to the user session, and validate them on return. Skipping this step leaves flows open to session hijacking.
3. Authorization code interception
Always use HTTPS. Enforce TLS 1.2 or higher. Combine the authorization code grant with PKCE, even for server-side apps, to neutralize code interception attacks.
4. Token scope minimization
Grant the smallest possible scope. Over-scoped tokens expand the blast radius if compromised. Regularly rotate tokens and expire them when unused.
5. Access token storage
Never store tokens in localStorage where JavaScript can read them. For web apps, prefer HTTP-only secure cookies. For mobile, use encrypted platform-specific stores.
6. Token introspection and revocation
Integrate token introspection to validate active sessions before each request. Support revocation endpoints to kill compromised tokens immediately.
A thorough OAuth 2.0 security review audits each step against known attack vectors. It tests how tokens are issued, stored, transmitted, and revoked. It validates that every redirect, parameter, and header is under control. This is not one checklist—it's a discipline, applied continuously in CI/CD, pre-production, and live environments.
Attackers know OAuth 2.0 better than most teams do. The difference is they test to exploit, while you must test to defend.
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