milaidy/claude-code-stealth.mjs at main · lawyered0/milaidy · GitHub

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/**
 * Claude Code Stealth Mode
 *
 * Monkey-patches global fetch to intercept Anthropic API requests made with
 * OAuth setup tokens (sk-ant-oat*). Mimics Claude Code's exact request pattern:
 *
 * 1. Replaces x-api-key with Authorization: Bearer
 * 2. Adds Claude Code beta headers
 * 3. Injects "You are Claude Code..." system prefix
 * 4. Sets Claude CLI user-agent
 *
 * This is loaded before the ElizaOS runtime so ALL Anthropic calls are patched,
 * regardless of which plugin/service makes them.
 */

const CLAUDE_CODE_VERSION = "2.1.2";
const CLAUDE_CODE_SYSTEM_PREFIX =
  "You are Claude Code, Anthropic's official CLI for Claude.";
const ANTHROPIC_BETA =
  "claude-code-20250219,oauth-2025-04-20,fine-grained-tool-streaming-2025-05-14,interleaved-thinking-2025-05-14";

function isOAuthToken(val) {
  return typeof val === "string" && val.includes("sk-ant-oat");
}

const originalFetch = globalThis.fetch;

globalThis.fetch = async function stealthFetch(input, init) {
  // Only intercept Anthropic API calls
  const url = typeof input === "string" ? input : input?.url || "";
  if (!url.includes("anthropic.com")) {
    return originalFetch(input, init);
  }

  if (!init) {
    return originalFetch(input, init);
  }

  // Check if we're using an OAuth token (via x-api-key or Authorization header)
  const headers = init.headers || {};
  const apiKey = headers["x-api-key"] || headers["X-Api-Key"];
  const existingAuth = headers.Authorization || headers.authorization;

  // Determine the token
  let token = null;
  if (apiKey && isOAuthToken(apiKey)) {
    token = apiKey;
  } else if (
    existingAuth &&
    isOAuthToken(existingAuth.replace("Bearer ", ""))
  ) {
    token = existingAuth.replace("Bearer ", "");
  }

  if (!token) {
    // Not an OAuth token, pass through normally
    return originalFetch(input, init);
  }

  // === STEALTH MODE: Mimic Claude Code exactly ===

  // 1. Fix headers: Bearer auth + Claude Code identity
  const newHeaders = { ...headers };
  delete newHeaders["x-api-key"];
  delete newHeaders["X-Api-Key"];
  newHeaders.Authorization = `Bearer ${token}`;
  newHeaders["anthropic-beta"] = ANTHROPIC_BETA;
  newHeaders["user-agent"] =
    `claude-cli/${CLAUDE_CODE_VERSION} (external, cli)`;
  newHeaders["x-app"] = "cli";
  newHeaders.accept = "application/json";
  newHeaders["anthropic-dangerous-direct-browser-access"] = "true";

  // 2. Inject system prompt prefix into request body
  if (typeof init.body === "string") {
    try {
      const body = JSON.parse(init.body);

      const prefix = { type: "text", text: CLAUDE_CODE_SYSTEM_PREFIX };

      if (Array.isArray(body.system)) {
        if (
          !body.system.some((s) => s.text?.startsWith("You are Claude Code"))
        ) {
          body.system.unshift(prefix);
        }
      } else if (typeof body.system === "string") {
        body.system = [prefix, { type: "text", text: body.system }];
      } else if (!body.system) {
        body.system = [prefix];
      }

      init.body = JSON.stringify(body);

      console.log(
        `[stealth] ${body.model} → Bearer auth + Claude Code system prefix (${body.system.length} blocks)`,
      );
    } catch {
      // Not JSON body, pass through
    }
  }

  init.headers = newHeaders;
  return originalFetch(input, init);
};

console.log(
  "[stealth] Claude Code stealth mode active — all Anthropic OAuth requests will be patched",
);