sc-auth

sc-auth is a skill for Claude Code, Codex from ersinkoc/security-check. It costs 19 tokens per session (1,170 once invoked), scanned A, original, MIT.

A security review guide for finding authentication weaknesses in web applications and APIs. Authentication is the process of checking who a user is, including password login, sessions, tokens, OAuth, API keys, and multi-factor authentication.

In plain words
What is it for?
Checking password rules, brute-force protection, password hashing, hardcoded credentials, login and session handling, token security, OAuth, API keys, and multi-factor authentication.
Why use it?
It helps reveal ways attackers could guess passwords, reuse stolen credentials, bypass login, abuse password resets, or exploit unsafe credential storage.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/ersinkoc/security-check/sc-auth
Any agent
npx skills add ersinkoc/security-check --skill sc-auth
Clone the repo
git clone --depth 1 https://github.com/ersinkoc/security-check

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for sc-auth

README.md
[![agentmods](https://agentmods.dev/badge/skills/ersinkoc/security-check/sc-auth.svg)](https://agentmods.dev/skills/ersinkoc/security-check/sc-auth)
Your own site
<a href="https://agentmods.dev/skills/ersinkoc/security-check/sc-auth"><img src="https://agentmods.dev/badge/skills/ersinkoc/security-check/sc-auth.svg" alt="Measured on agentmods" height="20"></a>
Per session 19 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,170 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00019 $0.01170
Opus 5 $0.00010 $0.00585
Sonnet 5 $0.00004 $0.00234
Haiku 4.5 $0.00002 $0.00117

Measured 5d ago against content hash b6b91872cfab, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

sc-auth scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 5d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

skills/sc-auth/SKILL.md · 136 lines

How it starts

The opening of the file, as written. The whole thing — 136 lines — stays where its author put it; the contents beside it link to each section on GitHub.

SC: Authentication Flaws

Purpose

Detects authentication vulnerabilities including weak password policies, missing brute force protection, insecure password storage, authentication bypass, hardcoded credentials, insecure password reset flows, and missing multi-factor authentication. Covers session-based, JWT, OAuth, and API key authentication models.

Activation

Called by sc-orchestrator during Phase 2. Runs against all web applications and APIs.

Phase 1: Discovery

File Patterns to Search

**/*auth*, **/*login*, **/*signin*, **/*signup*, **/*register*,
**/*password*, **/*credential*, **/*token*, **/*session*,
**/*oauth*, **/*mfa*, **/*2fa*, **/middleware/*, **/guards/*

Keyword Patterns to Search

# Password hashing
"md5(", "sha1(", "sha256(", "hashlib.md5", "hashlib.sha1",
"MessageDigest.getInstance(\"MD5\"", "MessageDigest.getInstance(\"SHA-1\"",
"bcrypt", "argon2", "scrypt", "pbkdf2", "password_hash(",
"crypto.createHash("

# Authentication logic
"password ==", "password ===", "password.equals(",
"authenticate(", "login(", "verify_password(", "check_password(",
"compareSync(", "compare("

# Hardcoded credentials
"password = \"", "password = '", "passwd", "secret",
"api_key = \"", "token = \"", "admin:admin", "root:root"

# Brute force protection
"rate_limit", "throttle", "max_attempts", "lockout",
"login_attempts", "failed_attempts"

Vulnerability Categories

1. Weak Password Hashing:

# VULNERABLE: MD5/SHA for password storage
password_hash = hashlib.md5(password.encode()).hexdigest()

# SAFE: bcrypt with appropriate cost factor
password_hash = bcrypt.hashpw(password.encode(), bcrypt.gensalt(rounds=12))

2. Missing Brute Force Protection:

// VULNERABLE: No rate limiting on login
app.post('/login', async (req, res) => {
  const user = await User.findOne({ email: req.body.email });
  if (user && await bcrypt.compare(req.body.password, user.password)) {
    return res.json({ token: generateToken(user) });
  }
  return res.status(401).json({ error: 'Invalid credentials' });
});

// SAFE: With rate limiting
const loginLimiter = rateLimit({ windowMs: 15 * 60 * 1000, max: 5 });
app.post('/login', loginLimiter, async (req, res) => { /* ... */ });

Read the full file on GitHub · 136 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 5d ago First seen · 136 lines · 19 tokens per session scan A b6b91872cfab

Subscribe to this mod's changes

sc-auth is a skill published in the GitHub repository ersinkoc/security-check (56 stars, last pushed 1mo ago), licensed MIT. It adds 19 tokens to every session and 1,170 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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