feat: enhance JWT algorithm confusion skill with ES256, sig2n, nonce reuse, deserialization RCE

[YVORYU]

Enhancement: JWT Algorithm Confusion Attack Skill

This PR significantly enhances the existing exploiting-jwt-algorithm-confusion-attack skill from v1.0.0 to v2.0.0, adding 5 new attack vectors, a full reconnaissance phase, executable helper scripts, and deep-dive reference files.

What's New

Category	Original (v1.0.0)	Enhanced (v2.0.0)
Attack vectors	5 steps	10 steps (Steps 0-9)
ES256 confusion	Not covered	Full coverage (4 EC key formats)
ECDSA nonce reuse	Not covered	Detection + private key recovery
sig2n (public key derivation)	Not covered	Docker tool + automated testing
JWT deserialization RCE	Not covered	Jackson enableDefaultTyping exploitation
KID path traversal (known files)	Only /dev/null	hostname, /proc/version, uploaded files
JKU attack closure	Payload only	Full: diagnostics, keypair, JWKS hosting, forge
HS256 brute-force	Not covered	hashcat/john/python + wordlist
KID SQLi	Listed payloads only	Two-stage attack (detect, exploit)
Reconnaissance phase	None	Step 0: endpoint discovery, credential hints, decision tree
Reference files	0	5 deep-dive reference files
Helper scripts	0	agent.py (500+ lines, 15 CLI commands)
Library/CVE mapping	None	14 libraries mapped to CVEs

Files Changed

• SKILL.md — Rewritten with 10-step workflow, decision tree, CVE mapping table
• scripts/agent.py — New: executable agent for all attack vectors
• references/recon.md — New: target reconnaissance and token acquisition
• references/header-injection.md — New: JKU/JWK/X5U/X5C/KID injection details
• references/bruteforce-sqli.md — New: HS256 brute-force and KID SQLi chains
• references/advanced-attacks.md — New: ES256, nonce reuse, sig2n, deserialization RCE, path traversal
• references/api-reference.md — New: quick-reference tables for all vectors

Compliance

• Follows CONTRIBUTING.md skill quality checklist
• Frontmatter: name (kebab-case), description with discovery keywords, domain/subdomain, tags, version, author (mahipal), contributors (YVORYU), license, nist_csf, mitre_attack
• Markdown sections: When to Use, Prerequisites, Workflow, Key Concepts, Tools & Systems, Common Scenarios, Output Format
• Original author preserved, enhancement contributor added