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.
npx skills add majiayu000/spellbook --skill auth-securitygit clone --depth 1 https://github.com/majiayu000/spellbookWrote 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.
[](https://agentmods.dev/skills/majiayu000/spellbook/auth-security)<a href="https://agentmods.dev/skills/majiayu000/spellbook/auth-security"><img src="https://agentmods.dev/badge/skills/majiayu000/spellbook/auth-security/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/majiayu000/spellbook/auth-security"><img src="https://agentmods.dev/badge/skills/majiayu000/spellbook/auth-security.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 8 findings, up to high
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- high Privilege Escalation · line 11 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- high Privilege Escalation · line 213 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- high Privilege Escalation · line 354 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- high Privilege Escalation · line 383 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- high Privilege Escalation · line 381 Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
- medium Data Exfiltration · line 61 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 353 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
- medium Data Exfiltration · line 362 Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00036 | $0.02814 |
| Opus 5.5 | $0.00014 | $0.01126 |
| Sonnet 5.5 | $0.00007 | $0.00563 |
| Haiku 4.5 | $0.00004 | $0.00281 |
Grade A, and why
auth-security scanned grade A with 1 finding 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 1mo 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.
Sends data to an external URLlowData exfiltration
A POST to an outside endpoint may be telemetry or may be exfiltration; either way the mod talks to somewhere, and you should know where.
const tokenResponse = await fetch('https://auth.example.com/token', { method: 'POST', Downgraded: this mod is about security review, or the phrase is quoted, so it is likely naming the pattern rather than instructing it.
How it starts
The opening of the file, as written. The whole thing — 433 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Auth Security
Core Principles
- OAuth 2.1 — Follow RFC 9700 (January 2025)
- PKCE Required — All clients must use PKCE
- Short-lived Tokens — Access tokens expire in 5-15 minutes
- Token Rotation — Refresh tokens are single-use
- HttpOnly Storage — Browser tokens in HttpOnly cookies
- Explicit Algorithm — Never trust JWT header algorithm
- No backwards compatibility — Delete deprecated auth flows
OAuth 2.1 Key Changes
Deprecated Flows (DO NOT USE)
| Flow | Status | Replacement |
|---|---|---|
| Implicit Grant | Removed | Authorization Code + PKCE |
| Password Grant | Removed | Authorization Code + PKCE |
| Auth Code without PKCE | Removed | Must use PKCE |
Required: Authorization Code + PKCE
import crypto from 'crypto';
// 1. Generate code verifier (43-128 chars)
function generateCodeVerifier(): string {
return crypto.randomBytes(32).toString('base64url');
}
// 2. Generate code challenge
function generateCodeChallenge(verifier: string): string {
return crypto
.createHash('sha256')
.update(verifier)
.digest('base64url');
}
// 3. Authorization request
const verifier = generateCodeVerifier();
const challenge = generateCodeChallenge(verifier);
const authUrl = new URL('https://auth.example.com/authorize');
authUrl.searchParams.set('response_type', 'code');
authUrl.searchParams.set('client_id', CLIENT_ID);
authUrl.searchParams.set('redirect_uri', REDIRECT_URI);
authUrl.searchParams.set('code_challenge', challenge);
authUrl.searchParams.set('code_challenge_method', 'S256');
authUrl.searchParams.set('scope', 'openid profile email');
authUrl.searchParams.set('state', generateState());
// 4. Token exchange (after redirect)
const tokenResponse = await fetch('https://auth.example.com/token', {
method: 'POST',
headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
body: new URLSearchParams({
grant_type: 'authorization_code',
code: authorizationCode,
redirect_uri: REDIRECT_URI,
client_id: CLIENT_ID,
code_verifier: verifier, // Prove we initiated the request
}),
});
What ships with it
4 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 1mo ago First seen · 433 lines · 36 tokens per session scan A 24467947c509
auth-security is a skill published in the GitHub repository majiayu000/spellbook (288 stars, last pushed yesterday), licensed MIT. It adds 36 tokens to every session and 2,814 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 1 finding (sends data to an external url). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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