feat: claude-code tokenization proxy with ggshield DLP

Local DLP proxy between claude-code and the Anthropic API. Scans outgoing /v1/messages bodies with ggshield, swaps detected secrets for opaque placeholder tokens, and restores them in the streamed SSE response on the fly. Licensed under AGPL-3.0-or-later.
2026-06-19 22:48:45 -04:00
commit bd138a8d12
11 changed files with 1193 additions and 0 deletions
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 #   ──────────────── Added by agents-init ──────────────────
 #   agents-init --agents
 AGENTS/
 /AGENTS.md
 /CLAUDE.md
 #   ────────────────────────────────────────────────────────
 #   ──────────────── Added by agents-init ──────────────────
 #   agents-init --plugins
 docs/superpowers
 docs/plans
 docs/specs
 docs/devlogs
 #   ────────────────────────────────────────────────────────
 node_modules/
 # ggshield local cache
 .cache_ggshield
@@ -0,0 +1,661 @@
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 interface could display a "Source" link that leads users to an archive
 of the code.  There are many ways you could offer source, and different
 solutions will be better for different programs; see section 13 for the
 specific requirements.
  You should also get your employer (if you work as a programmer) or school,
 if any, to sign a "copyright disclaimer" for the program, if necessary.
 For more information on this, and how to apply and follow the GNU AGPL, see
 <https://www.gnu.org/licenses/>.
@@ -0,0 +1,110 @@
 # claude-tokenization-proxy
 A local Data Loss Prevention (DLP) proxy that sits between `claude-code` and the
 Anthropic API. It scans outgoing requests for secrets with
 [GitGuardian's `ggshield`](https://github.com/GitGuardian/ggshield), swaps each
 secret for an opaque placeholder token before it leaves your machine, then
 restores the real secret in the streamed response on the fly — so Claude never
 sees your secrets but tooling that echoes a placeholder still gets the real
 value back.
 ```
 claude-code ──POST /v1/messages──► proxy ──redacted──► api.anthropic.com
                                     │  (ggshield scan, secret → <<<gg_token_…>>>)
 claude-code ◄──SSE (detokenized)─── proxy ◄──SSE stream──┘
                                     (<<<gg_token_…>>> → real secret, streaming)
 ```
 ## How it works
 1. **Request interception** — the JSON body of `POST /v1/messages` is scanned by
   `ggshield`. Every detected secret is replaced with a unique
   `<<<gg_token_[hex]>>>` placeholder, and the `token → secret` mapping is kept
   in memory (`src/store.ts`). The redacted body is forwarded upstream.
 2. **Streaming detokenization** — the Anthropic SSE response is piped through a
   stateful `Transform` (`src/detokenize.ts`) that scans the byte stream for
   placeholders and substitutes the original secret back. It holds back only the
   few characters that could still become a token, so a placeholder split across
   chunk boundaries (`…<<<gg_to` / `ken_abc>>>…`) is reassembled correctly.
 Secrets live only in memory for the lifetime of the process — restart the proxy
 and the mapping is gone.
 ## Requirements
 - **Node.js ≥ 23.6** (the proxy runs TypeScript directly via Node's built-in
  type stripping — no build step, no `ts-node`/`tsx`). On Node 22.6–23.5 run
  with `node --experimental-strip-types src/index.ts`.
 - **`ggshield`** on your `PATH` and authenticated (`ggshield auth login`). If
  `ggshield` is missing or errors, the proxy logs a warning and forwards traffic
  **unredacted** (fail-open) — it never blocks your requests.
 ## Setup
 ```bash
 npm install        # dev-only deps (TypeScript types); not needed to run
 npm start          # starts the proxy on http://127.0.0.1:8080
 ```
 Point `claude-code` at the proxy:
 ```bash
 export ANTHROPIC_BASE_URL=http://127.0.0.1:8080
 claude
 ```
 For the [fish shell](https://fishshell.com/):
 ```fish
 set -gx ANTHROPIC_BASE_URL http://localhost:8080
 claude
 ```
 That's the only change `claude-code` needs — it keeps using your normal
 `ANTHROPIC_API_KEY` / `x-api-key`, which the proxy forwards untouched.
 ## Configuration
 | Env var                 | Default            | Purpose                          |
 | ----------------------- | ------------------ | -------------------------------- |
 | `PORT`                  | `8080`             | Port the proxy listens on        |
 | `ANTHROPIC_UPSTREAM_HOST` | `api.anthropic.com` | Upstream API host to forward to |
 ## Tell Claude to leave the tokens alone
 So the model preserves placeholders verbatim (e.g. when writing them to files),
 copy [`templates/CLAUDE.md`](templates/CLAUDE.md) into the `CLAUDE.md` of any
 project you run `claude-code` in:
 ```markdown
 # Security Constraints
 Do not modify, remove, or evaluate strings formatted as `<<<gg_token_[a-z0-9]+>>>`.
 Treat them as opaque identifiers and preserve them exactly as they appear when
 writing or reading files.
 ```
 ## Scripts
 | Command           | What it does                                          |
 | ----------------- | ----------------------------------------------------- |
 | `npm start`       | Run the proxy                                         |
 | `npm run dev`     | Run with `--watch` (restarts on file changes)         |
 | `npm test`        | Run the detokenizer state-machine self-check          |
 | `npm run typecheck` | Type-check the source with `tsc --noEmit`           |
 ## Limitations
 - Detection is only as good as `ggshield`. It catches known secret patterns and
  generic high-entropy strings, not arbitrary sensitive prose.
 - Re-inserted secrets are assumed to be escape-neutral (typical API
  keys/tokens). A secret literally containing a backslash or double-quote could
  mis-escape inside the response JSON. See the `ponytail:` note in
  `src/detokenize.ts`.
 - The token map is in-memory only; it is not shared across proxy restarts or
  multiple proxy processes.
 ## License
 Copyright (C) 2026 Rootiest. Licensed under the
 [GNU Affero General Public License v3.0 or later](LICENSE).
@@ -0,0 +1,50 @@
 {
  "name": "claude-tokenization-proxy",
  "version": "1.0.0",
  "lockfileVersion": 3,
  "requires": true,
  "packages": {
    "": {
      "name": "claude-tokenization-proxy",
      "version": "1.0.0",
      "devDependencies": {
        "@types/node": "^24",
        "typescript": "^5.6"
      },
      "engines": {
        "node": ">=23.6"
      }
    },
    "node_modules/@types/node": {
      "version": "24.13.2",
      "resolved": "https://registry.npmjs.org/@types/node/-/node-24.13.2.tgz",
      "integrity": "sha512-fRa09kZTgu8o71KFcDjUFuc7F+dEbZYZmkI0mg5YBTRs0yMKjYHsq/c0urDKeDb+D5qVgXOdFcuu+DZPKOITwA==",
      "dev": true,
      "license": "MIT",
      "dependencies": {
        "undici-types": "~7.18.0"
      }
    },
    "node_modules/typescript": {
      "version": "5.9.3",
      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.3.tgz",
      "integrity": "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==",
      "dev": true,
      "license": "Apache-2.0",
      "bin": {
        "tsc": "bin/tsc",
        "tsserver": "bin/tsserver"
      },
      "engines": {
        "node": ">=14.17"
      }
    },
    "node_modules/undici-types": {
      "version": "7.18.2",
      "resolved": "https://registry.npmjs.org/undici-types/-/undici-types-7.18.2.tgz",
      "integrity": "sha512-AsuCzffGHJybSaRrmr5eHr81mwJU3kjw6M+uprWvCXiNeN9SOGwQ3Jn8jb8m3Z6izVgknn1R0FTCEAP2QrLY/w==",
      "dev": true,
      "license": "MIT"
    }
  }
 }
@@ -0,0 +1,21 @@
 {
  "name": "claude-tokenization-proxy",
  "version": "1.0.0",
  "private": true,
  "description": "Local DLP/tokenization proxy that strips secrets out of claude-code traffic via ggshield and restores them on the way back.",
  "license": "AGPL-3.0-or-later",
  "type": "module",
  "engines": {
    "node": ">=23.6"
  },
  "scripts": {
    "start": "node src/index.ts",
    "dev": "node --watch src/index.ts",
    "test": "node src/detokenize.ts --test",
    "typecheck": "tsc --noEmit"
  },
  "devDependencies": {
    "@types/node": "^24",
    "typescript": "^5.6"
  }
 }
@@ -0,0 +1,142 @@
 // Copyright (C) 2026 Rootiest
 // SPDX-License-Identifier: AGPL-3.0-or-later
 import { Transform, type TransformCallback } from "node:stream";
 import { StringDecoder } from "node:string_decoder";
 import { pathToFileURL } from "node:url";
 import { resolveToken as storeResolve } from "./store.ts";
 // Token shape: <<<gg_token_[0-9a-f]+>>>  (hex, because that's what we generate).
 const PREFIX = "<<<gg_token_";
 const SUFFIX = ">>>";
 const COMPLETE_RE = /^<<<gg_token_[0-9a-f]+>>>/;
 // Could `s` (which starts with '<') still grow into a token with more input?
 // True for any strict prefix of a well-formed token.
 function isPartialPrefix(s: string): boolean {
  if (PREFIX.startsWith(s)) return true; // still building the literal "<<<gg_token_"
  if (!s.startsWith(PREFIX)) return false;
  const rest = s.slice(PREFIX.length);
  // hex chars, then an optional partial of the ">>>" closer
  return /^[0-9a-f]*>{0,2}$/.test(rest);
 }
 /**
 * Stateful SSE detokenizer. Scans the raw upstream byte stream for our
 * placeholder tokens and swaps them back to the original secrets on the fly,
 * holding back only the few characters that could still become a token so
 * tokens split across chunk boundaries are reassembled correctly.
 */
 export class DetokenizeStream extends Transform {
  private buf = "";
  private decoder = new StringDecoder("utf8");
  private resolve: (token: string) => string | undefined;
  constructor(resolve: (token: string) => string | undefined = storeResolve) {
    super();
    this.resolve = resolve;
  }
  private emitFor(token: string): string {
    const secret = this.resolve(token);
    if (secret === undefined) return token; // unknown token: leave it untouched
    // ponytail: token appears inside a JSON string in the SSE `data:` line, so
    // re-escape. Assumes secrets are escape-neutral (typical API keys/tokens);
    // a secret literally containing a backslash or quote would double-escape —
    // upgrade to context-aware splicing if that ever bites.
    return JSON.stringify(secret).slice(1, -1);
  }
  override _transform(chunk: Buffer, _enc: BufferEncoding, cb: TransformCallback): void {
    this.buf += this.decoder.write(chunk);
    let out = "";
    while (this.buf.length > 0) {
      const lt = this.buf.indexOf("<");
      if (lt === -1) {
        out += this.buf;
        this.buf = "";
        break;
      }
      out += this.buf.slice(0, lt); // everything before '<' is safe to emit
      this.buf = this.buf.slice(lt); // buf now starts at the '<'
      const complete = COMPLETE_RE.exec(this.buf);
      if (complete) {
        out += this.emitFor(complete[0]);
        this.buf = this.buf.slice(complete[0].length);
        continue;
      }
      if (isPartialPrefix(this.buf)) break; // might finish next chunk; hold it
      // This '<' can't begin a token. Emit it and keep scanning past it.
      out += "<";
      this.buf = this.buf.slice(1);
    }
    cb(null, out);
  }
  override _flush(cb: TransformCallback): void {
    const out = this.buf + this.decoder.end();
    this.buf = "";
    cb(null, out);
  }
 }
 // --- self-check: `node src/detokenize.ts --test` -------------------------
 function runSelfTest(): void {
  const assert = (cond: boolean, msg: string) => {
    if (!cond) throw new Error("FAIL: " + msg);
  };
  const map = new Map([
    ["<<<gg_token_abc123>>>", "SUPER-SECRET-KEY"],
    ["<<<gg_token_dead>>>", "hunter2"],
  ]);
  const resolve = (t: string) => map.get(t);
  // Feed input split into arbitrary chunks, collect output.
  const run = (chunks: string[]): string => {
    const s = new DetokenizeStream(resolve);
    let out = "";
    s.on("data", (d) => (out += d.toString()));
    for (const c of chunks) s.write(Buffer.from(c, "utf8"));
    s.end();
    return out;
  };
  // 1. Token split across a chunk boundary (the critical case).
  assert(
    run(["password is <<<gg_to", "ken_abc123>>> done"]) ===
      "password is SUPER-SECRET-KEY done",
    "split token reassembled",
  );
  // 2. Token split one char at a time.
  assert(
    run("x <<<gg_token_dead>>> y".split("")) === "x hunter2 y",
    "char-by-char token",
  );
  // 3. Plain text with stray '<' and '<<<' that is NOT a token flushes promptly.
  assert(run(["a < b <<< c <<<not"]) === "a < b <<< c <<<not", "non-token < flushed");
  // 4. Unknown token passes through unchanged.
  assert(run(["see <<<gg_token_ffff>>>!"]) === "see <<<gg_token_ffff>>>!", "unknown token kept");
  // 5. Two tokens back to back.
  assert(
    run(["<<<gg_token_abc123>>><<<gg_token_dead>>>"]) === "SUPER-SECRET-KEYhunter2",
    "adjacent tokens",
  );
  // 6. Incomplete token at end of stream flushed verbatim.
  assert(run(["tail <<<gg_token_ab"]) === "tail <<<gg_token_ab", "incomplete token flushed on end");
  // 7. Overlapping '<' runs.
  assert(run(["<<<<gg_token_dead>>>"]) === "<hunter2", "leading extra angle bracket");
  console.log("detokenize self-test: all assertions passed");
 }
 if (process.argv[1] && import.meta.url === pathToFileURL(process.argv[1]).href) {
  runSelfTest();
 }
@@ -0,0 +1,77 @@
 // Copyright (C) 2026 Rootiest
 // SPDX-License-Identifier: AGPL-3.0-or-later
 import http from "node:http";
 import https from "node:https";
 import { tokenizeBody } from "./tokenize.ts";
 import { DetokenizeStream } from "./detokenize.ts";
 const PORT = Number(process.env.PORT) || 8080;
 const UPSTREAM_HOST = process.env.ANTHROPIC_UPSTREAM_HOST || "api.anthropic.com";
 // Headers we must not forward verbatim (they describe the OLD body/transport).
 const STRIP_REQ = new Set(["host", "content-length", "accept-encoding"]);
 const STRIP_RES = new Set(["content-length", "content-encoding", "transfer-encoding", "connection"]);
 function readBody(req: http.IncomingMessage): Promise<Buffer> {
  return new Promise((resolve, reject) => {
    const chunks: Buffer[] = [];
    req.on("data", (c) => chunks.push(c));
    req.on("end", () => resolve(Buffer.concat(chunks)));
    req.on("error", reject);
  });
 }
 function pick(headers: http.IncomingHttpHeaders, strip: Set<string>): http.OutgoingHttpHeaders {
  const out: http.OutgoingHttpHeaders = {};
  for (const [k, v] of Object.entries(headers)) {
    if (v !== undefined && !strip.has(k.toLowerCase())) out[k] = v;
  }
  return out;
 }
 const server = http.createServer(async (req, res) => {
  try {
    const isTarget = req.method === "POST" && (req.url ?? "").startsWith("/v1/messages");
    const rawBody = await readBody(req);
    // Only the messages endpoint carries user prompts worth scanning.
    const outBody = isTarget ? Buffer.from(await tokenizeBody(rawBody.toString("utf8")), "utf8") : rawBody;
    const headers = pick(req.headers, STRIP_REQ);
    headers["content-length"] = Buffer.byteLength(outBody);
    // Force identity so the SSE stream reaches the detokenizer uncompressed.
    headers["accept-encoding"] = "identity";
    const upstream = https.request(
      { host: UPSTREAM_HOST, port: 443, method: req.method, path: req.url, headers },
      (upRes) => {
        res.writeHead(upRes.statusCode ?? 502, pick(upRes.headers, STRIP_RES));
        if (isTarget) {
          // Detokenize the response body (SSE or JSON) on the way back.
          upRes.pipe(new DetokenizeStream()).pipe(res);
        } else {
          upRes.pipe(res);
        }
      },
    );
    upstream.on("error", (err) => {
      console.error("[proxy] upstream error:", err.message);
      if (!res.headersSent) res.writeHead(502, { "content-type": "text/plain" });
      res.end("Upstream request failed");
    });
    upstream.end(outBody);
  } catch (err) {
    console.error("[proxy] request error:", (err as Error).message);
    if (!res.headersSent) res.writeHead(500, { "content-type": "text/plain" });
    res.end("Proxy error");
  }
 });
 server.listen(PORT, "127.0.0.1", () => {
  console.log(`[proxy] DLP tokenization proxy listening on http://127.0.0.1:${PORT}`);
  console.log(`[proxy] forwarding to https://${UPSTREAM_HOST}`);
  console.log(`[proxy] point claude-code at it:  export ANTHROPIC_BASE_URL=http://127.0.0.1:${PORT}`);
 });
@@ -0,0 +1,12 @@
 // Copyright (C) 2026 Rootiest
 // SPDX-License-Identifier: AGPL-3.0-or-later
 // In-memory token <-> secret map. ponytail: a Map is enough; secrets live only
 // for the lifetime of the proxy process. Swap for SQLite only if you need
 // persistence across restarts (you almost certainly don't — secrets shouldn't
 // outlive the session).
 export const secrets = new Map<string, string>();
 export function resolveToken(token: string): string | undefined {
  return secrets.get(token);
 }
@@ -0,0 +1,83 @@
 // Copyright (C) 2026 Rootiest
 // SPDX-License-Identifier: AGPL-3.0-or-later
 import { spawn } from "node:child_process";
 import { randomBytes } from "node:crypto";
 import { mkdtemp, writeFile, rm } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { secrets } from "./store.ts";
 let ggshieldWarned = false;
 function newToken(): string {
  return `<<<gg_token_${randomBytes(8).toString("hex")}>>>`;
 }
 // Run ggshield over `text` and return the list of plaintext secret strings it
 // found. Returns [] (and warns once) if ggshield is missing or errors — fail
 // open so the proxy never blocks traffic, per the brief.
 async function scanSecrets(text: string): Promise<string[]> {
  let dir: string | undefined;
  try {
    dir = await mkdtemp(join(tmpdir(), "ggscan-"));
    const file = join(dir, "payload.txt");
    await writeFile(file, text, "utf8");
    const stdout = await new Promise<string>((resolve, reject) => {
      // ggshield 1.45 has no stdin scan mode, so we scan a temp file.
      // --show-secrets puts the plaintext in `match`; --all-secrets stops it
      // filtering example/known keys; exit code 1 just means "found secrets".
      const proc = spawn(
        "ggshield",
        ["secret", "scan", "--json", "--show-secrets", "--all-secrets", "path", file],
        { stdio: ["ignore", "pipe", "ignore"] },
      );
      let out = "";
      proc.stdout.on("data", (d) => (out += d));
      proc.on("error", reject); // ENOENT etc.
      proc.on("close", () => resolve(out));
    });
    const report = JSON.parse(stdout);
    const found = new Set<string>();
    for (const entity of report.entities_with_incidents ?? []) {
      for (const incident of entity.incidents ?? []) {
        for (const occ of incident.occurrences ?? []) {
          if (typeof occ.match === "string" && occ.match.length > 0) found.add(occ.match);
        }
      }
    }
    return [...found];
  } catch (err) {
    if (!ggshieldWarned) {
      ggshieldWarned = true;
      const reason = (err as NodeJS.ErrnoException).code === "ENOENT"
        ? "ggshield not found on PATH"
        : `ggshield scan failed: ${(err as Error).message}`;
      console.warn(`[proxy] WARNING: ${reason} — forwarding traffic WITHOUT secret redaction`);
    }
    return [];
  } finally {
    if (dir) await rm(dir, { recursive: true, force: true }).catch(() => {});
  }
 }
 /**
 * Scan a raw request body for secrets, replace each with a placeholder token,
 * record the token->secret mapping, and return the redacted body. Longest
 * secrets first so a secret that contains another is replaced whole.
 */
 export async function tokenizeBody(body: string): Promise<string> {
  const found = await scanSecrets(body);
  if (found.length === 0) return body;
  let redacted = body;
  for (const secret of found.sort((a, b) => b.length - a.length)) {
    if (!redacted.includes(secret)) continue;
    const token = newToken();
    secrets.set(token, secret);
    redacted = redacted.split(secret).join(token);
  }
  return redacted;
 }
@@ -0,0 +1,3 @@
 # Security Constraints
 Do not modify, remove, or evaluate strings formatted as `<<<gg_token_[a-z0-9]+>>>`. Treat them as opaque identifiers and preserve them exactly as they appear when writing or reading files.
@@ -0,0 +1,14 @@
 {
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "allowImportingTsExtensions": true,
    "noEmit": true,
    "strict": true,
    "esModuleInterop": true,
    "skipLibCheck": true,
    "types": ["node"]
  },
  "include": ["src"]
 }
		`@@ -0,0 +1,3 @@`
							`# Security Constraints`

							Do not modify, remove, or evaluate strings formatted as `<<<gg_token_[a-z0-9]+>>>`. Treat them as opaque identifiers and preserve them exactly as they appear when writing or reading files.