Method unsign

src/server/web/auth/adapter.ts:133–149

* Verifies the HMAC and returns the raw session ID, or null on failure. * Uses constant-time comparison to prevent timing attacks.

(signed: string)

   * Uses constant-time comparison to prevent timing attacks.
   */
  unsign(signed: string): string | null {
    const dot = signed.lastIndexOf(".");
    if (dot === -1) return null;
    const id = signed.slice(0, dot);
    const provided = signed.slice(dot + 1);

    const hmac = createHmac("sha256", this.key);
    hmac.update(id);
    const expected = hmac.digest("base64url");

    if (provided.length !== expected.length) return null;
    let diff = 0;
    for (let i = 0; i < provided.length; i++) {
      diff |= provided.charCodeAt(i) ^ expected.charCodeAt(i);
    }
    return diff === 0 ? id : null;
  }

  // ── Request / response helpers ────────────────────────────────────────────