Learn API Security Testing: From Zero to API Penetration Testing Master

Goal: Deeply understand API security vulnerabilities, testing methodologies, and exploitation techniques—from basic authentication flaws to advanced injection attacks and business logic bypasses. You will learn to identify and exploit OWASP API Top 10 vulnerabilities, master broken authentication and authorization (BOLA/BFLA/BOPLA), perform JWT attacks, conduct NoSQL and SQL injection against APIs, test GraphQL endpoints with introspection and DoS techniques, exploit SSRF vulnerabilities, and build secure APIs that resist these attacks. By the end, you’ll be able to conduct professional API security assessments using both manual and automated techniques, understand the attacker mindset, build custom security tools, and design resilient APIs that protect against modern threats. You’ll develop the mental models necessary to think like both an attacker and a defender, understanding not just how to find vulnerabilities but why they exist and how to prevent them at the architectural level.

Introduction

APIs (Application Programming Interfaces) are the connective tissue of the modern internet, powering everything from mobile apps and microservices to IoT devices, B2B integrations, and cloud-native architectures. However, this ubiquity has made them the #1 attack vector for web applications. In 2024, APIs account for over 80% of all web traffic, and 91% of organizations reported API security incidents. The average cost of an API-related breach is $4.88 million,demonstrating the critical importance of API security expertise.

In this guide, you will move beyond traditional web security (XSS, CSRF) to master the unique challenges of API security. You will build your own testing tools from scratch, analyze vulnerable applications, understand the business logic behind authorization flaws, and learn the mindset of an API hacker. This is not just about running automated scanners—it’s about understanding the deep principles that make APIs vulnerable and developing the expertise to find zero-day vulnerabilities.

What You Will Build:

You will create a comprehensive API Security Testing Arsenal consisting of 20 specialized tools and scripts—from a BOLA hunter and JWT cracker to a full-featured API reconnaissance framework. Each tool will teach you fundamental concepts while giving you practical skills applicable to bug bounty hunting, penetration testing, and secure development.

The API Security Landscape

Traditional Web App                    Modern API-First Architecture
┌─────────────────────┐               ┌─────────────────────────────────┐
│   Browser ──► Web   │               │  Mobile App ──┐                │
│   Server (HTML)     │               │               │                │
│                     │               │  Web SPA ─────┼───► API ──► DB │
└─────────────────────┘               │               │    Gateway     │
                                      │  IoT Device ──┤                │
Single attack surface                 │               │                │
(mostly server-side rendering)        │  Partner ─────┘                │
                                      └─────────────────────────────────┘
                                      Multiple attack surfaces, same API
                                      Client-side logic, rich data exposure

Scope (what’s included):

OWASP API Security Top 10 (2023) vulnerabilities
Authentication and authorization attacks
Injection attacks (SQL, NoSQL, Command, SSRF)
GraphQL security testing
Rate limiting and DoS attacks
Business logic vulnerabilities
API reconnaissance and discovery
Automated security tool development

Out of scope (for this guide):

Web application security basics (assumed knowledge)
Mobile app reverse engineering (though we’ll test mobile APIs)
Infrastructure security beyond API gateways
Compliance frameworks (SOC2, HIPAA)—though we’ll mention them

Key Terms You’ll See Everywhere

API Gateway: Centralized entry point for all API traffic, often handling authentication, rate limiting, and routing
Bearer Token: Authentication token sent in the HTTP Authorization header, typically a JWT
Endpoint: A specific URL path that accepts API requests (e.g., /api/v1/users)
Payload: The data sent in an API request body, usually in JSON format
Schema: The structure definition of API requests and responses (OpenAPI/Swagger)

How to Use This Guide

Read the Theory Primer First: The “Mini-Book” section below covers the deep concepts you need. Don’t skip it—API security is subtle, and understanding the why is as important as the how. Each concept includes real-world examples, mental models, and check-your-understanding questions.
Build the Projects in Order: The projects are sequenced to build your skills layer by layer. Start with reconnaissance, move to authorization attacks (the most common vulnerabilities), then authentication, injection, and finally integration projects. Each project builds on concepts from previous ones.
Focus on the “Core Question”: Each project answers a specific conceptual question. Ensure you can answer it before moving on. This ensures you’re building deep understanding, not just copying code.
Use the “Definition of Done”: Don’t just copy code. Verify your tools work against real vulnerable targets (like OWASP crAPI, Juice Shop, or DVWA). Test edge cases and document your findings.
Practice Ethically: Everything in this guide should only be used against systems you own or have explicit written permission to test. Build your own vulnerable labs or use intentionally vulnerable applications.

Prerequisites & Background Knowledge

Essential Prerequisites (Must Have)

HTTP Fundamentals:

Methods (GET, POST, PUT, PATCH, DELETE) and when each is used
Headers (Authorization, Content-Type, User-Agent, X-Forwarded-For, etc.)
Status Codes: 2xx (success), 3xx (redirect), 4xx (client error), 5xx (server error)
Understanding of cookies vs tokens vs sessions
How HTTPS differs from HTTP

Data Formats:

JSON structure, parsing, and validation
XML basics (for SOAP APIs)
Understanding of data type coercion issues

REST API Concepts:

Resources and endpoints
Statelessness principle
CRUD operations mapping to HTTP methods
Query parameters vs path parameters vs request body

Command Line Basics:

Comfortable with curl, wget, and jq
Basic scripting (Python or Bash)
Environment variables and configuration files

Basic Scripting:

Python: requests library, json module, basic error handling
Ability to parse command-line arguments
File I/O operations

Helpful But Not Required

OAuth 2.0 / OIDC:

Authorization Code flow
Client Credentials flow
Refresh tokens and access tokens
Can learn during: Project 9 (OAuth Attacks)

GraphQL:

Query syntax and mutations
Schema structure
Can learn during: Projects 4, 13 (GraphQL)

Database Knowledge:

SQL basics (SELECT, WHERE, UNION)
NoSQL (MongoDB) query syntax
Can learn during: Projects 5, 14 (Injection)

Docker:

Running containers
Docker Compose for multi-container setups
Can learn during: All projects (for running vulnerable targets)

Self-Assessment Questions

Before starting, verify your readiness:

✅ Can you explain the difference between Authentication (who you are) and Authorization (what you can do)?
✅ Can you decode a JWT manually and explain its three parts (header, payload, signature)?
✅ Can you use curl to send a POST request with a JSON body and a custom Authorization header?
✅ Do you know what an IDOR (Insecure Direct Object Reference) is? (Hint: It’s the old name for BOLA)
✅ Can you explain why {"user_id": 1} in a request body might be a security issue?

If you answered “no” to questions 1-3: Spend 1-2 weeks studying HTTP fundamentals and basic web security before starting. Read “The Web Application Hacker’s Handbook” Ch. 1-4.

If you answered “yes” to all 5: You’re ready to begin!

Development Environment Setup

OS: Linux (Kali/Ubuntu), macOS, or Windows (WSL2)

Languages:

Python 3.11+ (primary language for most projects)
Node.js 18+ (for some targets and Projects 4, 13)
Go 1.21+ (optional, for performance-critical tools)

Tools:

Essential:

Burp Suite Community/Pro: Industry standard intercepting proxy
Postman: For legitimate API interaction and baseline testing
curl: Command-line HTTP client
jq: JSON processor for parsing API responses
Docker: To run vulnerable apps and isolated test environments

Recommended:

OWASP ZAP: Free alternative to Burp Suite
jwt_tool: JWT manipulation and testing
Arjun: HTTP parameter discovery tool
ffuf: Fast web fuzzer
httpie: User-friendly HTTP client
mitmproxy: Scriptable intercepting proxy
Postman/Newman: Automated API testing

Python Libraries:

pip install requests pyjwt python-jose colorama urllib3 beautifulsoup4 tqdm

Vulnerable Practice Applications:

# OWASP crAPI (Completely Ridiculous API)
git clone https://github.com/OWASP/crAPI
cd crAPI
docker-compose up

# VAmPI (Vulnerable API)
docker run -p 5000:5000 erev0s/vampi

# Damn Vulnerable Web Services (DVWS)
git clone https://github.com/snoopysecurity/dvws-node
cd dvws-node
npm install && npm start

Testing Your Setup:

# Test Python environment
python3 --version  # Should be 3.11+
python3 -c "import requests, jwt; print('Libraries OK')"

# Test curl and jq
curl https://httpbin.org/get | jq '.headers'

# Test Burp Suite is running
curl http://localhost:8080 --proxy http://127.0.0.1:8080 2>&1 | grep -q "Burp" && echo "Burp OK"

# Test Docker
docker run hello-world

Time Investment

Theory Primer: 6-8 hours (don’t skip this!)
Simple projects (1, 4, 12, 15, 18, 19): 4-8 hours each
Moderate projects (2, 3, 6, 7, 8, 10, 13, 14): 10-20 hours each
Complex projects (5, 9, 11, 16, 17): 20-40 hours each
Capstone (20): 40-60 hours
Total Mastery: 4-8 months of consistent study and practice (2-4 hours per day, 4-5 days per week)

Important Reality Check

WARNING: This guide teaches offensive security techniques. NEVER test APIs you do not own or have explicit written permission to test. Unauthorized testing violates the Computer Fraud and Abuse Act (CFAA) in the US and similar laws globally. It is illegal and unethical.

Legal and Ethical Usage:

Test only your own applications
Use intentionally vulnerable applications (crAPI, VAmPI, DVWA)
Participate in authorized bug bounty programs (HackerOne, Bugcrowd) within scope
Get written authorization for penetration testing engagements
Report vulnerabilities responsibly through proper disclosure channels

API security is hard. These concepts are production-grade security engineering. Don’t expect to understand everything immediately. The learning happens in layers:

First pass: Get the tool working (copy-paste is okay to start)
Second pass: Understand what each piece does
Third pass: Understand why it’s designed that way
Fourth pass: See the security implications and edge cases
Fifth pass: Modify and improve the tool for your specific needs

Big Picture / Mental Model

The API Attack Pipeline

Understanding the phases of an API attack helps you structure your testing methodology and tools:

   1. Reconnaissance        2. Authentication       3. Authorization       4. Exploitation
   ┌────────────────┐       ┌────────────────┐      ┌────────────────┐     ┌────────────────┐
   │ Find Endpoints │       │ Bypass Auth    │      │ Escalate Privs │     │ Inject/Abuse   │
   │                │       │                │      │                │     │                │
   │ - Fuzzing      │──────►│ - Weak JWTs    │─────►│ - BOLA (IDOR)  │────►│ - Injection    │
   │ - Docs (OpenAPI│       │ - OAuth Flaws  │      │ - BFLA         │     │ - Mass Assign  │
   │ - Mobile Apps  │       │ - Cred Stuffing│      │ - BOPLA        │     │ - DoS          │
   │ - Source Code  │       │ - Token Leaks  │      │ - Logic Flaws  │     │ - SSRF         │
   └────────────────┘       └────────────────┘      └────────────────┘     └────────────────┘
           │                        │                       │                      │
           ▼                        ▼                       ▼                      ▼
    Map the Surface          Gain Access             Access Data            Compromise System

Phase 1: Reconnaissance - You can’t hack what you can’t see. This phase is about discovering:

All API endpoints (documented and hidden)
API versions (current, deprecated, and “shadow” APIs)
Authentication mechanisms
Input validation rules
Rate limiting policies

Phase 2: Authentication - Testing how the API verifies identity:

Credential attacks (stuffing, brute force)
Token attacks (JWT manipulation, theft)
Session management flaws
Multi-factor authentication bypasses

Phase 3: Authorization - The hardest and most common vulnerability class:

BOLA: Can I access other users’ data?
BFLA: Can I perform admin functions?
BOPLA: Can I read/write sensitive fields?
This is where most vulnerabilities exist because authorization logic is custom and complex

Phase 4: Exploitation - Leveraging vulnerabilities for impact:

Injection attacks (SQL, NoSQL, command, SSRF)
Business logic abuse
Denial of service
Mass assignment and data exposure

Theory Primer (Mini-Book)

This section is your textbook. Read it carefully before building the projects. Each concept includes real-world examples, mental models, and implications.

Chapter 1: The OWASP API Security Top 10 (2023) - Deep Dive

Fundamentals

The OWASP API Security Top 10 is the definitive awareness document for the most critical security risks to APIs. Unlike the OWASP Web Application Top 10, which focuses on traditional web vulnerabilities (XSS, CSRF, etc.), the API Top 10 specifically addresses the unique security challenges introduced by APIs: machine-to-machine communication, rich data exposure, and complex authorization logic.

The 2023 update reflects the evolution of API threats, with significant focus on authorization issues (BOLA, BFLA, BOPLA now account for 3 of the top 5 risks) and business logic abuse (newly added as API6:2023). This shift acknowledges that API attacks have moved beyond simple technical exploits to sophisticated abuse of business workflows.

Why APIs Are Different:

Implicit trust in authenticated requests: Traditional web apps often re-verify permissions on every page render. APIs often assume “if you’re logged in, you can access this endpoint.”
Rich data exposure: APIs return structured data (JSON/XML) containing far more information than UI displays, trusting the client to filter it.
Business logic at the edge: APIs expose business workflows directly, without the protective layer of server-side rendering and session management.
M2M communication: Many API consumers are other services, not humans, changing the threat model significantly.

Deep Dive into Each Vulnerability

1. API1:2023 - Broken Object Level Authorization (BOLA)

BOLA is the undisputed king of API vulnerabilities, responsible for approximately 78.2% of major API incidents in 2024 and leading to over 1.6 billion leaked records in 2024 alone (an 80% increase from 2023).

What it is: BOLA occurs when an API endpoint exposes a reference to an internal object (like a user ID, invoice ID, or document ID) but fails to validate that the authenticated user has permission to access that specific object.

The Mental Model:

User A (authenticated) ───► GET /api/invoices/1002 ───► API Server
                                                          │
                                                          ▼
                                      [Check: Is User A logged in?] ✓ YES
                                      [Check: Does invoice 1002 belong to User A?] ✗ MISSING!
                                                          │
                                                          ▼
                                      Returns Invoice 1002 (belongs to User B)
                                      ★ DATA LEAK ★

Why it happens:

Developers assume clients won’t change IDs: They trust the UI to only show IDs the user owns
Authorization checks are complex: Checking “Is user logged in?” is easy (one line). Checking “Does this specific object belong to this specific user?” requires database queries and business logic
Rapid development pressure: In agile sprints, authorization logic gets deferred as “we’ll add that later”
Microservices complexity: In distributed systems, the service handling the request might not know about user ownership

Real-World Examples:

Trello (January 2024): An unauthenticated API endpoint allowed attackers to link private emails to public Trello accounts by simply knowing the email address. Impact: 15 million users exposed. The endpoint /1/members/{username} didn’t verify that the requester had permission to see the email-to-username mapping.

Dell (May 2024): Partner portal API lacked adequate object-level access controls. Attackers created fake partner accounts and accessed customer data by iterating customer IDs. Impact: 49 million customer records compromised. The endpoint /api/customer/{id} only checked if the requester was authenticated, not if they were authorized for that specific customer.

PandaBuy (April 2024): Multiple API authorization flaws enabled access to sensitive shipping data by manipulating order IDs. Impact: 1.3 million customers. Attackers found they could access /api/orders/{order_id} with any authenticated account, regardless of who placed the order.

Peloton (2021, still frequently cited): Any authenticated user could access other users’ private data (including weight, height, workout history) by manipulating the user_id parameter in /api/user/{user_id}/overview. This exposed millions of users’ personal health information.

How to test for BOLA:

Two-account technique: Create two accounts (User A and User B)
Capture traffic as User A: Record all IDs in responses (user_id, resource_id, etc.)
Replay as User B: Replace User A’s IDs with User B’s IDs
Analyze responses: If you get 200 OK with User A’s data while logged in as User B, you’ve found BOLA

Attack vectors:

Sequential IDs: /api/users/1, /api/users/2, /api/users/3
UUIDs (if they leak elsewhere): /api/documents/a7b3-c8d9-e1f2...
Encoded IDs: Base64-encoded integers are still predictable
Nested resources: /api/users/1/documents/5 - check authorization at BOTH levels

Defense mechanisms:

# BAD (only checks authentication)
@require_login
def get_invoice(invoice_id):
    return Invoice.get(invoice_id)

# GOOD (checks both authentication AND authorization)
@require_login
def get_invoice(invoice_id):
    invoice = Invoice.get(invoice_id)
    if invoice.user_id != current_user.id:
        abort(403)  # Forbidden
    return invoice

Common Misconceptions:

“UUIDs prevent BOLA”: False. If UUIDs leak anywhere (logs, analytics, referrer headers), they’re as exploitable as sequential IDs
“OAuth protects against BOLA”: False. OAuth handles authentication, not authorization
“API gateways prevent BOLA”: False. Gateways can’t know your business logic about who owns what

Check Your Understanding:

Why is BOLA harder to detect with automated scanners than SQL injection?
An API uses JWTs containing user_id. Does this prevent BOLA? Why or why not?
You find an endpoint /api/admin/users/{id} that returns 403 for regular users. Is this BOLA-proof?

Check Your Understanding - Answers:

BOLA requires understanding business logic and user relationships. Scanners can’t know if User A should access Resource X without context about ownership. SQL injection has universal payloads.
No. The JWT proves who you are, not what you can access. The API still needs to check if you own the requested resource.
Not necessarily. It prevents BFLA (function-level), but you still need to test if an admin can access other admins’ data. Check /api/admin/users/{other_admin_id}.

Real-World Applications:

E-commerce: Accessing other users’ orders, carts, payment methods
Healthcare: HIPAA violations from accessing other patients’ records
SaaS platforms: Accessing other organizations’ data, configurations, billing info
Financial services: Viewing other users’ transactions, account balances, statements

Where You’ll Apply This:

Project 2: BOLA Hunter (core focus)
Project 8: BFLA Scanner (distinguishes vertical vs horizontal auth)
Project 20: Capstone Pentest (integrating BOLA testing into full methodology)

Key Insight: Authentication is not authorization. Just because someone is logged in doesn’t mean they should access any logged-in data. Every object access must verify ownership.

2. API2:2023 - Broken Authentication

Fundamentals: Broken authentication allows attackers to compromise authentication tokens, exploit implementation flaws, or bypass authentication mechanisms entirely. Unlike BOLA which is about authorization (what you can access), broken authentication is about impersonation (becoming someone else).

Deep Dive:

Authentication in APIs is different from traditional web applications:

Stateless nature: APIs typically don’t use cookies and sessions. They use tokens (JWT, OAuth access tokens, API keys)
Long-lived tokens: Unlike session cookies that expire quickly, API tokens often last hours, days, or never expire
Exposed to multiple clients: APIs serve web, mobile, IoT—each with different security characteristics
Machine-to-machine: Service accounts need authentication without human interaction

The Attack Surface:

Registration → Login → Token Generation → Token Storage → Token Transmission → Token Validation
     ↓            ↓            ↓                ↓                ↓                    ↓
  No email   Weak pwd     Weak secret    Client storage   Unencrypted      No expiry check
  verify     No rate      Predictable    Local storage    HTTP             No revocation
            limit        algorithm       Logs             Referrer          No rotation
            No MFA       "none" accepted Git commits      Debug output      No signature check

Common Broken Authentication Vulnerabilities:

1. Credential Attacks:

Credential Stuffing: Using leaked credentials from other breaches
Brute Force: Trying common passwords without rate limiting
Default Credentials: API keys like admin/admin or default OAuth secrets
Password Reset Flaws: Token reuse, predictable tokens, no expiration

2. Token Vulnerabilities:

Weak JWT Secrets: Secrets like “secret”, “password”, or short keys susceptible to brute force
None Algorithm: Accepting {"alg": "none"} which removes signature verification entirely
Algorithm Confusion: Switching from RS256 (asymmetric) to HS256 (symmetric) using the public key as the HMAC secret
No Expiration: Tokens that never expire or have very long lifetimes
Token Leakage: Tokens in URLs, logs, analytics, error messages

3. OAuth 2.0 Flaws:

Open Redirect: Manipulating redirect_uri to steal authorization codes
Missing State Parameter: CSRF attacks on OAuth flows
Implicit Flow: Tokens in URL fragments leak via Referer header
Client Secret Exposure: Hardcoded secrets in mobile apps or JavaScript

Mental Model - JWT Authentication Flow:

1. Login
   User ──[username, password]──► API Server
                                      │
                                      ▼
                            Verify credentials in database
                                      │
                                      ▼
                            Generate JWT with user_id
                            Sign with secret key
                                      │
                                      ▼
   User ◄──[JWT token]────────────── API Server

2. Authenticated Request
   User ──[GET /api/data]──────────► API Server
          [Authorization: Bearer JWT]    │
                                         ▼
                                   Verify JWT signature
                                   Check expiration
                                   Extract user_id
                                         │
                                         ▼
                                   Process request
                                         │
                                         ▼
   User ◄──[Response data]───────────── API Server

Real-World Examples:

Major Breaches:

T-Mobile (2023): API authentication bypass allowed attackers to access 37 million customer records
Optus (2022, Australia): Unauthenticated API endpoint exposed 11 million customer records. No authentication required at all on a public-facing endpoint.

Common Scenarios:

Peloton (2020): Account takeover via authentication token stored in predictable location
Numerous bug bounties: JWT secrets like “secret”, “test”, “password123” found in production APIs

How Attackers Exploit Broken Authentication:

JWT Attack Example:

# Original JWT (decoded)
{
  "alg": "HS256",
  "typ": "JWT"
}
{
  "sub": "user_123",
  "role": "user",
  "exp": 1704067200
}

# Attack 1: None algorithm
# Change header to:
{
  "alg": "none",
  "typ": "JWT"
}
# Change payload to:
{
  "sub": "user_123",
  "role": "admin",  # Escalate privilege
  "exp": 1904067200  # Far future
}
# Remove signature, send to server
# If accepted: Complete authentication bypass

# Attack 2: Weak secret brute force
$ python jwt_tool.py [token] -C -d wordlist.txt
# If secret is "secret123":
[+] secret123

# Now forge any token:
{
  "sub": "admin",
  "role": "admin",
  "exp": 1999999999
}
# Sign with "secret123", full compromise

Defense Mechanisms:

Strong Authentication:

# Good JWT implementation
import jwt
from datetime import datetime, timedelta

# NEVER use weak secrets
JWT_SECRET = os.environ['JWT_SECRET']  # 256-bit random key
JWT_ALGORITHM = 'HS256'  # Explicitly set
ALLOWED_ALGORITHMS = ['HS256']  # Whitelist only

def create_token(user_id):
    payload = {
        'sub': user_id,
        'iat': datetime.utcnow(),  # Issued at
        'exp': datetime.utcnow() + timedelta(hours=1),  # Expires in 1 hour
        'jti': uuid.uuid4().hex  # Unique token ID for revocation
    }
    return jwt.encode(payload, JWT_SECRET, algorithm=JWT_ALGORITHM)

def verify_token(token):
    try:
        payload = jwt.decode(
            token,
            JWT_SECRET,
            algorithms=ALLOWED_ALGORITHMS,  # Explicit whitelist
            options={
                'verify_signature': True,  # MUST verify
                'verify_exp': True,  # Check expiration
                'require': ['exp', 'sub', 'iat']  # Required claims
            }
        )
        # Check if token is revoked (in Redis/database)
        if is_token_revoked(payload['jti']):
            raise AuthenticationError('Token revoked')
        return payload
    except jwt.ExpiredSignatureError:
        raise AuthenticationError('Token expired')
    except jwt.InvalidTokenError:
        raise AuthenticationError('Invalid token')

Rate Limiting:

# Prevent brute force attacks
from flask_limiter import Limiter

limiter = Limiter(
    app,
    key_func=lambda: request.remote_addr,
    default_limits=["100 per hour"]
)

@app.route('/api/login', methods=['POST'])
@limiter.limit("5 per minute")  # Only 5 login attempts per minute
def login():
    # ... authentication logic ...
    pass

Common Misconceptions:

“HTTPS prevents token theft”: HTTPS protects transmission, but doesn’t prevent client-side XSS, logging, or storage issues
“Long tokens are secure tokens”: Length doesn’t matter if the secret is weak or the algorithm is broken
“OAuth means it’s secure”: OAuth is a framework. Implementations can still be broken.

Check Your Understanding:

Your API uses 6-character API keys. Is this a broken authentication issue? Why?
You find a JWT with {"alg": "HS256"} and crack the secret in 10 seconds. What was likely the problem?
An API accepts both passwords and OAuth tokens. Which attack vectors should you test?

Check Your Understanding - Answers:

Yes. 6 characters = 62^6 (letters + numbers) = ~57 billion combinations. Modern GPUs can test billions per second. Should be minimum 32 random characters (256 bits).
The secret was either extremely short (< 8 characters) or a dictionary word. HS256 with strong secrets (32+ random bytes) is essentially uncrackable.
Both! Test password endpoints for brute force, credential stuffing, and weak password policy. Test OAuth for redirect_uri manipulation, state parameter bypass, and token leakage.

Real-World Applications:

API Key Management: Rotating keys, secure generation, revocation mechanisms
Token Storage: Secure storage in mobile apps, web apps, server-to-server
Session Management: Handling refresh tokens, token expiration, logout
MFA Integration: Adding second factor without breaking API workflows

Where You’ll Apply This:

Project 3: JWT Attack Toolkit (core focus)
Project 9: OAuth 2.0 Flow Attacks (OAuth-specific authentication)
Project 15: API Key Leakage Scanner (credential exposure)
Project 16: Broken Authentication Suite (comprehensive auth testing)
Project 20: Capstone (integrating authentication testing)

Key Insight: Authentication is the gateway. If it fails, everything fails. But authentication alone is not enough—you must still validate authorization for every resource access.