Borrowing it
Nothing to install: this file belongs to cardstack/boxel. 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/cardstack/boxel/main/.claude/skills/realm-auth/SKILL.mdgit clone --depth 1 https://github.com/cardstack/boxelWrote 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/cardstack/boxel/realm-auth)<a href="https://agentmods.dev/skills/cardstack/boxel/realm-auth"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/realm-auth/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/cardstack/boxel/realm-auth"><img src="https://agentmods.dev/badge/skills/cardstack/boxel/realm-auth.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 | $0.00196 | $0.03961 |
| Opus 5.5 | $0.00078 | $0.01584 |
| Sonnet 5.5 | $0.00039 | $0.00792 |
| Haiku 4.5 | $0.00020 | $0.00396 |
Grade A, and why
realm-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.
How it starts
The opening of the file, as written. The whole thing — 270 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Realm auth — token families and their invariants
The governing fact: every boxel token except the matrix access token is a stateless bearer JWT. Verification is a signature check, an expiry check, and a small number of claim comparisons against live database state. There is no session table and no token store, so nothing can be looked up, listed, or counted — only signed and later re-derived. Every design consequence below follows from that.
Matrix is the root authority. Minting any boxel token requires proving control of a matrix account (an openid token exchange), and Synapse is the only party that can genuinely revoke — its access tokens are real server-side sessions. Boxel tokens are derived credentials with their own, weaker retirement story.
The token families
| Token | Minted by | Claims | Lifetime |
|---|---|---|---|
| matrix access token | Synapse | n/a | no expiry by default |
| realm-server session | POST /_server-session |
{user, sessionRoom} |
SESSION_TOKEN_TTL (24h), or EXTENDED_SESSION_TOKEN_TTL (7d) on request |
| per-realm session | POST /_realm-auth, and the realm's own session route |
{user, realm, permissions, sessionRoom, realmServerURL} |
SESSION_TOKEN_TTL |
| delegated | POST /_delegate-session |
same, plus delegated: true, permissions: ['read'] |
DELEGATED_TOKEN_TTL (30m) |
| prerender service | buildCreatePrerenderAuth (in-process) |
per-realm session shape, plus realmAuthority: true (see below) |
1d |
| publish-realm | handle-publish-realm (in-process) |
per-realm session shape | 1h |
| diagnostic | POST /_diagnostic-render-token (operator token) |
prerender shape, plus diagnostic: {id, note, card, scope, realm}, permissions: ['read'] |
DIAGNOSTIC_SESSION_LIFETIME_SEC (15m) |
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.
- 5d ago First seen · 270 lines · 196 tokens per session scan A 5e90e2f0ffc5
realm-auth is a skill published in the GitHub repository cardstack/boxel (27 stars, last pushed today), licensed MIT. It adds 196 tokens to every session and 3,961 once invoked, about $0.0008 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 2026-10-21.
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