# Threat Model Outline for oauth2 Ruby Gem

## 1. Overview
This document outlines the threat model for the `oauth2` Ruby gem, which implements OAuth 2.0, 2.1, and OIDC Core protocols. The gem is used to facilitate secure authorization and authentication in Ruby applications.

## 2. Assets to Protect
- OAuth access tokens, refresh tokens, and ID tokens
- User credentials (if handled)
- Client secrets and application credentials
- Sensitive user data accessed via OAuth
- Private keys and certificates (for signing/verifying tokens)

## 3. Potential Threat Actors
- External attackers (internet-based)
- Malicious OAuth clients or resource servers
- Insiders (developers, maintainers)
- Compromised dependencies

## 4. Attack Surfaces
- OAuth endpoints (authorization, token, revocation, introspection)
- HTTP request/response handling
- Token storage and management
- Configuration files and environment variables
- Dependency supply chain

## 5. Threats and Mitigations

### 5.1 Token Leakage
- **Threat:** Tokens exposed via logs, URLs, or insecure storage
- **Mitigations:**
  - Avoid logging sensitive tokens
  - Use secure storage mechanisms
  - Never expose tokens in URLs

### 5.2 Token Replay and Forgery
- **Threat:** Attackers reuse or forge tokens
- **Mitigations:**
  - Validate token signatures and claims
  - Use short-lived tokens and refresh tokens
  - Implement token revocation

### 5.3 Insecure Communication
- **Threat:** Data intercepted via MITM attacks
- **Mitigations:**
  - Enforce HTTPS for all communications
  - Validate SSL/TLS certificates

### 5.4 Client Secret Exposure
- **Threat:** Client secrets leaked in code or version control
- **Mitigations:**
  - Store secrets in environment variables or secure vaults
  - Never commit secrets to source control

### 5.5 Dependency Vulnerabilities
- **Threat:** Vulnerabilities in third-party libraries
- **Mitigations:**
  - Regularly update dependencies
  - Use tools like `bundler-audit` for vulnerability scanning

### 5.6 Improper Input Validation
- **Threat:** Injection attacks via untrusted input
- **Mitigations:**
  - Validate and sanitize all inputs
  - Use parameterized queries and safe APIs

### 5.7 Request-Target Trust Boundary Expansion
- **Threat:** Applications may pass untrusted or insufficiently validated absolute URLs into request paths that can carry OAuth credentials or authenticated state.
- **Risk:** This can expand trust boundaries, contributing to token leakage, authenticated requests to unintended hosts, or SSRF-like pivoting in the surrounding application.
- **Mitigations:**
  - Prefer relative paths where practical
  - Do not pass untrusted absolute URLs into token-bearing clients
  - Validate or allowlist outbound request targets at the application layer
  - Treat request-target validation as a separate concern from log redaction and token storage

### 5.8 Insufficient Logging and Monitoring
- **Threat:** Attacks go undetected
- **Mitigations:**
  - Log security-relevant events (without sensitive data)
  - Monitor for suspicious activity

## 6. Assumptions
- The gem is used in a secure environment with up-to-date Ruby and dependencies
- End-users are responsible for secure configuration and deployment

## 7. Out of Scope
- Security of external OAuth providers
- Application-level business logic

## 8. References
- [OAuth 2.0 Threat Model and Security Considerations (RFC 6819)](https://tools.ietf.org/html/rfc6819)
- [OWASP Top Ten](https://owasp.org/www-project-top-ten/)

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This outline should be reviewed and updated regularly as the project evolves.
