testing-mobile-api-authentication

name	testing-mobile-api-authentication
description	Tests authentication and authorization mechanisms in mobile application APIs to identify broken authentication, insecure token management, session fixation, privilege escalation, and IDOR vulnerabilities. Use when performing API security assessments against mobile app backends, testing JWT implementations, evaluating OAuth flows, or assessing session management. Activates for requests involving mobile API auth testing, token security assessment, OAuth mobile flow testing, or API authorization bypass.
domain	cybersecurity
subdomain	mobile-security
author	mahipal
tags	["mobile-security","android","ios","api-security","authentication","penetration-testing"]
version	1.0.0
license	Apache-2.0

Testing Mobile API Authentication

When to Use

Use this skill when:

• Assessing mobile app backend API authentication during penetration tests
• Testing JWT token implementation for common vulnerabilities (none algorithm, weak signing)
• Evaluating OAuth 2.0 / OIDC flows in mobile applications for redirect, PKCE, and scope issues
• Testing for broken object-level authorization (BOLA/IDOR) in API endpoints

Do not use this skill against production APIs without explicit authorization and rate-limiting awareness.

Prerequisites

• Burp Suite or mitmproxy configured as mobile device proxy
• SSL pinning bypassed on target application (if implemented)
• Valid test account credentials for the target application
• Postman or curl for API request crafting
• jwt.io or PyJWT for JWT analysis and manipulation

Workflow

Step 1: Map Authentication Endpoints

Intercept mobile app traffic to identify authentication-related endpoints:

POST /api/v1/auth/login          - Initial authentication
POST /api/v1/auth/register       - Account registration
POST /api/v1/auth/refresh        - Token refresh
POST /api/v1/auth/logout         - Session termination
POST /api/v1/auth/forgot-password - Password reset
POST /api/v1/auth/verify-otp     - OTP verification
GET  /api/v1/auth/me             - Authenticated user profile

Step 2: Analyze Token Format and Security

JWT Analysis:

# Decode JWT without verification
echo "eyJhbGciOiJIUzI1NiIs..." | cut -d. -f2 | base64 -d 2>/dev/null

# Check for common JWT vulnerabilities:
# 1. None algorithm attack
# Change header to: {"alg":"none","typ":"JWT"}
# Remove signature: header.payload.

# 2. Algorithm confusion (RS256 to HS256)
# If server uses RS256, try HS256 with public key as secret

# 3. Weak signing key
# Use hashcat or jwt-cracker to brute-force HMAC secret
hashcat -m 16500 jwt.txt wordlist.txt

# 4. Expiration bypass
# Modify "exp" claim to future timestamp