# OAuth and OIDC Security Lab
OAuth 2.0 and OpenID Connect (OIDC) represent the backbone of modern application authentication and authorization, yet their complexity creates numerous attack vectors that practitioners often overlook. This security lab provides hands-on experience identifying and exploiting common vulnerabilities in OAuth implementations, from authorization code interception to JWT manipulation attacks. By understanding these weaknesses through controlled testing environments, security professionals can better evaluate production systems and implement robust defensive measures that protect against real-world exploitation attempts.
OAuth 2.0 is an authorization framework that enables applications to obtain limited access to user accounts on HTTP services. OpenID Connect builds upon OAuth 2.0 to provide authentication services, creating an identity layer that allows clients to verify user identity and obtain basic profile information. Together, these protocols handle billions of authentication events daily across web applications, mobile apps, and API services.
The OAuth and OIDC Security Lab focuses specifically on implementation vulnerabilities rather than protocol design flaws. This includes misconfigurations in authorization servers, improper client validation, token handling errors, and security control bypasses. The lab scope encompasses authorization code flows, implicit flows, client credentials flows, and hybrid flows, with particular emphasis on public client vulnerabilities.
This lab is not a general authentication testing framework. It does not cover SAML vulnerabilities, traditional session management flaws, or password-based authentication attacks. The scope excludes social engineering attacks against OAuth providers and focuses purely on technical exploitation of protocol implementation gaps. The lab also distinguishes between OAuth 2.0 authorization mechanics and OIDC authentication extensions, ensuring practitioners understand when they are testing authorization policies versus identity verification processes.
Key variants include Authorization Code flow with PKCE (Proof Key for Code Exchange), Implicit flow (now deprecated), Client Credentials flow for service-to-service authentication, and Device Authorization flow for input-constrained devices. Each variant presents distinct attack surfaces and requires different testing approaches within the lab environment.
The OAuth and OIDC Security Lab operates through controlled vulnerability injection in realistic application environments. The lab begins with establishing a complete authentication ecosystem using either Keycloak open-source identity management or Auth0 development instances as the authorization server. These platforms provide full OAuth 2.0 and OIDC support while allowing security researchers to modify configurations and introduce vulnerabilities intentionally.
The core lab infrastructure includes multiple client applications representing different OAuth client types: confidential clients (traditional web applications with server-side components), public clients (single-page applications and mobile apps), and hybrid scenarios. Each client application implements different OAuth flows, creating diverse testing scenarios. For example, a React-based single-page application demonstrates public client vulnerabilities, while a Node.js backend service showcases confidential client attack vectors.
Traffic interception capabilities form the foundation of most lab exercises. Tools like Burp Suite Professional, OWASP ZAP, or mitmproxy capture HTTP requests and responses between clients, authorization servers, and resource servers. This interception reveals token exchanges, redirect URI handling, and state parameter management that attackers target in real-world scenarios.
The Authorization Code flow testing exercise demonstrates the most critical OAuth vulnerability class. Participants configure intentionally vulnerable redirect URI validation, allowing attackers to steal authorization codes through open redirects or subdomain takeovers. The lab provides multiple target applications with different redirect URI validation flaws: wildcard matching (accepting any subdomain), path traversal vulnerabilities (allowing additional path components), and complete validation bypass. Practitioners learn to craft malicious URLs that redirect authorization codes to attacker-controlled domains, then exchange these codes for access tokens.
Token leakage exercises expand beyond simple redirect manipulation. The lab includes scenarios where access tokens appear in server logs due to improper GET parameter handling, browser history exposure through implicit flow usage, and referrer header leakage when applications navigate to external resources while authenticated. One specific scenario involves a vulnerable single-page application that receives tokens via URL fragments but logs all client-side errors (including full URLs) to a third-party service, inadvertently exposing user tokens.
Scope escalation testing reveals how improper authorization server configuration allows privilege elevation. The lab provides OAuth scopes with overlapping permissions and clients with excessive default scope grants. Participants modify authorization requests to claim additional scopes, test scope inheritance between different client applications, and exploit scope validation bypass vulnerabilities. For instance, a mobile application might request basic profile access but receive administrative permissions due to server-side scope validation errors.
JWT manipulation exercises target the cryptographic components of OIDC implementations. The lab includes authorization servers with weak JWT validation, supporting both RS256 (RSA signatures) and HS256 (HMAC signatures) algorithms. This configuration enables algorithm confusion attacks where participants convert RS256 tokens to HS256, using the authorization server's public RSA key as an HMAC secret. Additional JWT attacks include signature stripping (removing the signature and using unsigned tokens), key identifier (kid) manipulation to reference attacker-controlled keys, and claims tampering to modify user permissions or identity information.
PKCE (Proof Key for Code Exchange) implementation testing focuses on public client protection mechanisms. The lab provides both compliant and vulnerable PKCE implementations, allowing practitioners to understand proper code verifier generation, code challenge creation, and verification processes. Vulnerable scenarios include predictable code verifier generation, missing code challenge validation, and downgrade attacks that bypass PKCE entirely when clients support both PKCE and non-PKCE flows.
Refresh token rotation testing examines long-term token security. The lab implements various refresh token strategies: single-use refresh tokens that invalidate after use, reusable refresh tokens with extended lifetimes, and hybrid approaches. Participants test refresh token theft scenarios, token replay attacks, and refresh token leakage through insecure storage. One practical exercise involves extracting refresh tokens from mobile application local storage and demonstrating persistent account access even after password changes.
OAuth and OIDC vulnerabilities directly impact millions of user accounts and sensitive business data across modern applications. Poor implementation of these protocols creates authentication bypasses, unauthorized data access, and complete account takeovers that attackers actively exploit in production environments. The distributed nature of OAuth, involving multiple parties and network communications, multiplies the potential attack surface beyond traditional single-system authentication mechanisms.
Real-world OAuth exploitation has compromised major platforms repeatedly. In 2020, researchers discovered that Slack's OAuth implementation allowed subdomain takeover attacks to steal user authorization codes, potentially granting attackers access to private Slack workspaces and sensitive communications. The vulnerability stemmed from overly permissive redirect URI validation that accepted any subdomain under slack.com, including expired or vulnerable subdomains that attackers could control. This incident demonstrates how seemingly minor configuration errors create significant security exposures.
The business impact extends beyond individual account compromises. OAuth vulnerabilities often provide lateral movement opportunities within enterprise environments. When business applications use OAuth for single sign-on integration, successful exploitation can grant attackers access to multiple systems through a single compromised token. Financial services, healthcare organizations, and technology companies face regulatory compliance violations and customer trust erosion when OAuth implementations fail to protect user data adequately.
Common practitioner misconceptions compound these risks significantly. Many developers assume that OAuth providers handle all security responsibilities, neglecting client-side validation and secure token storage requirements. Others believe that HTTPS encryption alone protects OAuth flows, overlooking application-layer vulnerabilities like redirect URI manipulation and token leakage through logs or analytics services. Some organizations implement OAuth without understanding the differences between authorization and authentication, creating authorization bypass vulnerabilities when applications treat OAuth access tokens as proof of user identity without proper OIDC implementation.
The complexity of modern OAuth ecosystems creates additional blind spots. Applications often integrate multiple OAuth providers (Google, Microsoft, Facebook) with different security characteristics and configuration requirements. Developers may secure one integration properly while introducing vulnerabilities in others, creating inconsistent security postures. Mobile applications face particular challenges with secure token storage and deep link handling that web applications do not encounter.
Automated security testing tools frequently miss OAuth-specific vulnerabilities because they require understanding of application-specific business logic and multi-step authentication flows. This gap means organizations often deploy OAuth implementations with critical vulnerabilities that remain undetected until attackers exploit them in production environments.
The Cyber Defense Army approaches OAuth and OIDC security through the Identity and Access Technology (IAT) domain within the Planetary Defense Model, treating authentication protocols as critical infrastructure that requires continuous verification and zero-trust principles. Under the Zero Possession Architecture methodology, CDA assumes that all tokens, credentials, and authentication artifacts are compromised from the moment of creation, designing defensive strategies that function effectively even when core authentication mechanisms fail.
CDA's approach differs fundamentally from conventional OAuth security by rejecting the premise that proper implementation alone provides adequate protection. While traditional security frameworks focus on securing OAuth flows and preventing token leakage, CDA assumes tokens will be compromised and implements detection, containment, and response mechanisms that activate when authentication systems are breached. This includes real-time token usage monitoring, behavioral analysis of authenticated sessions, and automated response capabilities that can revoke compromised credentials within seconds of detecting anomalous activity.
The IAT domain integration requires treating OAuth and OIDC security as part of broader identity fabric rather than isolated authentication components. CDA practitioners implement cross-protocol correlation that detects when attackers use stolen OAuth tokens in conjunction with other compromised credentials or attempt to escalate privileges across different authentication boundaries. This holistic view reveals attack patterns that single-protocol monitoring systems miss entirely.
Operationally, CDA implements continuous OAuth security validation through automated testing pipelines that execute security lab scenarios against production configurations without disrupting legitimate user activities. These tests include synthetic authorization flows that verify redirect URI validation, automated token manipulation attempts that confirm JWT signature verification, and simulated public client attacks that validate PKCE implementation. Unlike traditional penetration testing that occurs periodically, CDA's approach provides continuous security posture verification.
The Zero Possession principle extends to OAuth implementation by designing systems that function securely even when authorization servers, client applications, or communication channels are compromised. This includes implementing token binding mechanisms that tie tokens to specific client instances, deploying mutual TLS authentication that prevents token theft from being immediately useful to attackers, and using short-lived tokens with aggressive rotation policies that minimize exposure windows.
CDA's defensive implementation includes distributed token validation that does not rely solely on authorization server responses, client-side anomaly detection that identifies unusual OAuth flow patterns, and automated incident response that can isolate compromised accounts before damage occurs. This multi-layered approach ensures that OAuth security failures do not cascade into broader system compromises.
• Implement PKCE for all OAuth public clients, including single-page applications and mobile apps, regardless of whether the authorization server requires it, as this protection prevents authorization code interception attacks even when other security controls fail.
• Validate redirect URIs using exact string matching rather than pattern matching or subdomain wildcards, and maintain a strictly controlled allowlist of permitted redirect endpoints that cannot be modified through application configuration files or environment variables.
• Configure access tokens with maximum lifetimes of 15 minutes and implement automated refresh token rotation on every use, ensuring that stolen tokens provide minimal attack windows and compromised refresh tokens become unusable quickly.
• Verify JWT signatures and validate all claims (issuer, audience, expiration, not-before) on every token use, never accepting tokens without signature verification even for seemingly low-risk operations, as unsigned tokens enable complete authentication bypass.
• Monitor OAuth flows for anomalous patterns including unusual geographic locations, rapid token refresh cycles, and authorization requests from unexpected client applications, implementing automated response capabilities that can revoke suspicious tokens within seconds of detection.
• JWT Security Testing Framework • API Authentication Bypass Techniques • Mobile Application Token Storage Analysis • Single Sign-On Security Architecture • Web Application Session Management • Multi-Factor Authentication Implementation
• IETF RFC 6749: The OAuth 2.0 Authorization Framework. https://tools.ietf.org/html/rfc6749
• IETF RFC 8252: OAuth 2.0 for Native Apps (Best Current Practice). https://tools.ietf.org/html/rfc8252
• NIST Special Publication 800-63B: Authentication and Lifecycle Management. https://pages.nist.gov/800-63-3/sp800-63b.html
• OWASP OAuth 2.0 Security Cheat Sheet. https://cheatsheeet.owasp.org/cheatsheets/OAuth2_Cheat_Sheet.html
• MITRE ATT&CK Framework: Valid Accounts (T1078). https://attack.mitre.org/techniques/T1078/