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docs/api-stack/api/api-plugin-vault/src/plugin/unlock.md

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+# plugin/unlock
+
+## Purpose
+
+Tiny helper module that owns the "where does the vault unlock secret
+come from?" question. The plugin's default `unlockExtractor` reads the
+`X-Vault-Unlock` request header, but operators with JWT-bound secrets,
+cookie-bound secrets, or password-derived flows override the extractor
+when constructing the plugin. `extractUnlock(c, extractor)` is the
+canonical call site invoked by every mutating route — it raises a typed
+`VaultPluginError(VAULT_PLUGIN_UNLOCK_HEADER_MISSING)` (400) when the
+extractor returns `null`.
+
+## Features
+
+- `headerExtractor(headerName)` — factory returning a
+  `VaultUnlockExtractor` that reads the named header. Header lookup is
+  case-insensitive per RFC 7230.
+- `defaultUnlockExtractor` — the canonical default used when the
+  plugin's options do not specify one: reads `X-Vault-Unlock`.
+- `extractUnlock(c, extractor)` — invokes the extractor and converts
+  `null` into a typed `VaultPluginError` so the host error handler
+  surfaces a clean 400 response.
+- Extracted secrets are returned to the caller; the module DOES NOT
+  log or persist them. The §13a security audit explicitly forbids
+  logging the unlock secret.
+
+## Usage: Basic
+
+```ts
+import {
+    defaultUnlockExtractor,
+    extractUnlock,
+    headerExtractor,
+} from "@suaveplan/api-plugin-vault";
+
+const unlockSecret = extractUnlock(c, defaultUnlockExtractor);
+const handle = await vaultService.openForPrincipal(principal, unlockSecret);
+```
+
+## Usage: Advanced
+
+```ts
+// JWT-bound unlock: extract a hashed password from a custom claim.
+const jwtExtractor: VaultUnlockExtractor = (c) => {
+    const auth = c.req.header("Authorization");
+    if (!auth?.startsWith("Bearer ")) return null;
+    const token = auth.slice(7);
+    try {
+        const payload = JSON.parse(
+            Buffer.from(token.split(".")[1] ?? "", "base64").toString("utf8")
+        ) as { vaultSecret?: string };
+        return payload.vaultSecret ?? null;
+    } catch {
+        return null;
+    }
+};
+
+const plugin = createVaultPlugin({
+    storage,
+    unlockExtractor: jwtExtractor,
+});
+```
+
+## API Reference
+
+### `headerExtractor(headerName: string): VaultUnlockExtractor`
+
+Returns an extractor that reads `headerName` from the request. Trims
+the value; returns `null` if the header is absent or empty after
+trimming.
+
+### `defaultUnlockExtractor: VaultUnlockExtractor`
+
+Pre-built extractor reading `X-Vault-Unlock`.
+
+### `extractUnlock(c: Context, extractor: VaultUnlockExtractor): string`
+
+Calls the extractor; raises `VaultPluginError(VAULT_PLUGIN_UNLOCK_HEADER_MISSING)`
+(400) when it returns `null`. The returned string is the unlock secret
+and MUST be passed directly to `vaultService.openForPrincipal`.
+
+## Implementation Notes
+
+- The unlock secret is NEVER logged. Both `defaultUnlockExtractor` and
+  the example custom extractors above only read; they do not emit.
+- `headerExtractor` validates the header value is a non-empty trimmed
+  string. Whitespace-only values count as absent because operators
+  occasionally inject `X-Vault-Unlock:` placeholders during testing —
+  trimming catches those.
+- The header name is forwarded verbatim to Hono's
+  `c.req.header(headerName)`; Hono performs case-insensitive matching
+  per the HTTP spec, so callers can supply any casing.
+- Returning the secret as a plain string (rather than wrapping it in a
+  `SecureBuffer`) is a deliberate trade-off: the unlock secret has the
+  same lifetime as the request handler, and adding a heap-allocated
+  wrapper imposes per-request allocator pressure without preventing a
+  memory dump from disclosing the value.