Borrowing it
Nothing to install: this file belongs to greenpau/go-authcrunch. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/greenpau/go-authcrunch/main/.codex/skills/authentication-portal-mfa/SKILL.mdgit clone --depth 1 https://github.com/greenpau/go-authcrunchWrote 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/greenpau/go-authcrunch/authentication-portal-mfa)<a href="https://agentmods.dev/skills/greenpau/go-authcrunch/authentication-portal-mfa"><img src="https://agentmods.dev/badge/skills/greenpau/go-authcrunch/authentication-portal-mfa/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/greenpau/go-authcrunch/authentication-portal-mfa"><img src="https://agentmods.dev/badge/skills/greenpau/go-authcrunch/authentication-portal-mfa.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.01320 |
| Opus 5.5 | $0.00014 | $0.00528 |
| Sonnet 5.5 | $0.00007 | $0.00264 |
| Haiku 4.5 | $0.00004 | $0.00132 |
Grade A, and why
authentication-portal-mfa 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 28d 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.
How it starts
The opening of the file, as written. The whole thing — 110 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Authentication Portal MFA
Ownership and login evidence
handle_http_sandbox.go and handle_json_login.go own login checkpoints;
webauthn_enrollment.go and the profile U2F API handlers own registration state.
pkg/identity owns credential validation, durable TOTP consumption and mutation.
The collaborating contracts are
local database transactions for durable
mutation and canonical login evidence for
identity binding. Authentication challenge policies
own conditional selection, user-transform/parser APIs, and AMR issuance. Successful
verification sets the server-only Checkpoint.Method; enrollment never does.
JSON hardware authentication must retain its server challenge and pass the actual
assertion to the backend, including when U2F is the first checkpoint.
After generating a JSON WebAuthn assertion challenge, return immediately and
wait for its signed response. Do not visit later password/TOTP checkpoints or
set authentication evidence during challenge issuance. Cover WebAuthn before,
after, and between other factors through HTML and JSON, including generic MFA
selection and additive password requirements.
Keep required factor types distinct. A totp checkpoint cannot pass with U2F, and a u2f checkpoint cannot pass with TOTP; only generic mfa permits selection. Seed every MFA backend operation with the original server-held LoginEvidence, including lockout check/increment/reset and TOTP consumption. Authentication can clear request evidence on failure; restore the original proof before counting a failure. A password reset, role change, revocation or replacement must prevent old sandboxes from consuming codes or mutating the current account's lockout.
Cross-realm lockout E2E tests must establish fresh password evidence for each attempt: refreshing a database alias can invalidate its older sandbox epoch. Keep separate stale-sandbox tests proving rejected evidence cannot consume a code or increment current lockout state. Invalid TOTP fixtures must exclude accepted neighboring time steps as well as the current code.
What ships with it
1 file 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.
- 28d ago Changed · +6 lines 825765067e35
- 1mo ago Changed · +16 lines 6373935aedba
- 1mo ago Changed · +18 lines d0c95e4120e3
- 1mo ago First seen · 70 lines · 36 tokens per session scan A 9a364ee1b555
authentication-portal-mfa is a skill published in the GitHub repository greenpau/go-authcrunch (60 stars, last pushed 10d ago), licensed Apache-2.0. It adds 36 tokens to every session and 1,320 once invoked, about $0.0001 per session on Opus 5.5. 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 2026-09-18.
authentication-portal-mfa compared with skills from other repositories
| Mod | Type | Stars | Last push | Licence | Scan | Tokens | Works with |
|---|---|---|---|---|---|---|---|
| authentication-portal-mfagreenpau/go-authcrunch | Skill | 60 | 10d ago | Apache-2.0 | A | 36 | Codex |
| imagegenopenai/codex | Skill | 133k | yesterday | Apache-2.0 | A | 113 | Codex |
| playwright-climicrosoft/playwright | Skill | 99k | yesterday | Apache-2.0 | A | 19 | Claude Code |
| local-ai-agentsmicrosoft/ai-agents-for-beginners | Skill | 79k | 4d ago | MIT | A | 200 | Claude Code, Codex |
| systematic-debuggingobra/superpowers | Skill | 313k | 3d ago | MIT | A | 21 | Claude Code |
| next-cache-components-adoptionvercel/next.js | Skill | 143k | yesterday | MIT | A | 95 | Claude Code |
| next-partial-prefetching-adoptionvercel/next.js | Skill | 143k | yesterday | MIT | A | 103 | Claude Code |