Testing API Authentication Weaknesses

# Testing API Authentication Weaknesses

## When to Use

- Assessing REST API authentication mechanisms for bypass vulnerabilities before production deployment
- Testing JWT token implementation for common weaknesses (none algorithm, key confusion, missing expiration)
- Evaluating whether all API endpoints enforce authentication or if some are unintentionally exposed
- Testing API key generation, storage, and rotation mechanisms for predictability or leakage
- Validating session management including token expiration, revocation, and refresh token security

**Do not use** without written authorization. Authentication testing involves attempting to bypass security controls.

## Prerequisites

- Written authorization specifying target API and authentication mechanisms in scope
- Valid test credentials for at least two user roles (regular user, admin)
- Burp Suite Professional with JWT-related extensions (JSON Web Tokens, JWT Editor)
- Python 3.10+ with `requests`, `PyJWT`, and `jwt` libraries
- Wordlists for credential testing (SecLists authentication wordlists)
- API documentation or OpenAPI specification

## Workflow

### Step 1: Authentication Mechanism Identification

```python
import requests
import json

BASE_URL = "https://target-api.example.com/api/v1"

# Probe the API to identify authentication mechanisms
auth_indicators = {
    "jwt_bearer": False,
    "api_key_header": False,
    "api_key_query": False,
    "basic_auth": False,
    "oauth2": False,
    "session_cookie": False,
    "custom_token": False,
}

# Test 1: Check unauthenticated access
resp = requests.get(f"{BASE_URL}/users/me")
print(f"Unauthenticated: {resp.status_code}")
if resp.status_code == 200:
    print("[CRITICAL] Endpoint accessible without authentication")

# Test 2: Check WWW-Authenticate header
if "WWW-Authenticate" in resp.headers: