orchestrator/agent-team/scripts/assert_no_write_token.py

#!/usr/bin/env python3
"""assert_no_write_token.py — fail closed if a GitHub *write* token is on the box.

The agent-team apply/verify path mints its ``pull-requests: write`` GitHub App
installation token **inside the CI runner** (via SHA-pinned
``actions/create-github-app-token``), from the ``AGENT_APPLY_APP_ID`` /
``AGENT_APPLY_APP_PRIVATE_KEY`` **Actions secrets**. By design the always-on
R720 box holds **no standing write credential**: it triggers CI with the
operator's host ``gh`` auth and reads results with a *read-only* token
(``AGENT_TEAM_CI_READ_TOKEN`` / ``GITHUB_TOKEN``). See ``ci/README.md`` and
``docs/P3-PHASE0-DESIGN.md`` ("the box holds no standing write token").

This audit asserts that invariant. It is runnable both on the box (as a
provisioning/runtime self-check) and in CI (as a regression guard). It:

  1. scans the live process environment (``os.environ``) and the coordinator's
     environment-derived config for token-shaped variables that would grant
     ``pull-requests: write`` / ``contents: write``;
  2. greps the box's local credential files (``~/secrev.env`` and
     ``~/orchestrator/.env`` by default; paths are configurable) for the App id
     and for any PEM private-key header (RSA / EC / OPENSSH / PKCS#8);

and **exits non-zero with a clear message** if any are found, or exits ``0``
with a short summary otherwise.

Usage::

    python -m scripts.assert_no_write_token
    python scripts/assert_no_write_token.py --env-file ~/secrev.env --env-file ~/x.env

Exit codes:
    0  no write-shaped token / App secret / private key found
    1  at least one finding (the box is mis-provisioned — remediate before deploy)
"""

from __future__ import annotations

import argparse
import os
import re
import sys
from collections.abc import Mapping, Sequence
from pathlib import Path

# --------------------------------------------------------------------------- #
# What "must never live on the box" looks like.
# --------------------------------------------------------------------------- #

# The GitHub App that holds ``pull-requests: write`` lives ONLY as Actions
# secrets. Its id and private key must never appear on the box (env or files).
APP_ID_ENV = "AGENT_APPLY_APP_ID"
APP_PRIVATE_KEY_ENV = "AGENT_APPLY_APP_PRIVATE_KEY"

# Env vars that are explicitly the App's write credentials.
_FORBIDDEN_ENV_VARS: frozenset[str] = frozenset(
    {
        APP_ID_ENV,
        APP_PRIVATE_KEY_ENV,
    }
)

# Env vars that are KNOWN-GOOD read-only / non-write and must NOT be flagged by
# the heuristic name match below (they are tokens, but read-only by contract).
_ALLOWED_TOKEN_ENV_VARS: frozenset[str] = frozenset(
    {
        "AGENT_TEAM_CI_READ_TOKEN",  # read-only CI-result fetcher token
        "AGENT_TEAM_API_TOKEN",  # read-only dashboard/API bearer
        "SLACK_APP_TOKEN",  # Slack socket-mode app-level token (not GitHub)
        "SLACK_BOT_TOKEN",  # Slack bot token (not GitHub)
        "CLAUDE_CODE_OAUTH_TOKEN",  # Anthropic subscription OAuth (not GitHub)
        "ANTHROPIC_API_KEY",  # model API key (not GitHub)
    }
)

# A name-shaped heuristic for "this looks like a GitHub *write* token". We
# deliberately scope to GitHub-write shapes so the generic read-only
# ``GITHUB_TOKEN`` fallback (a runtime read token, not a standing write secret)
# is not a false positive while the App's write material always is.
_WRITE_TOKEN_NAME_RE = re.compile(
    r"(?:^|_)(?:GH|GITHUB)_(?:APP|PAT|WRITE|APPLY)_?(?:TOKEN|KEY|PRIVATE_KEY)?",
    re.IGNORECASE,
)

# Value shapes that indicate a GitHub write-capable credential regardless of the
# var's name. ``ghp_`` (classic PAT) and ``github_pat_`` (fine-grained PAT) can
# both carry write scopes; an installation token (``ghs_``) is write-capable; a
# user-to-server token (``ghu_``) acts with the user's write access; and a refresh
# token (``ghr_``) mints fresh write-capable user-to-server tokens. All are
# write-risk material that must not live on the box.
_WRITE_TOKEN_VALUE_RE = re.compile(
    r"\b(?:ghp_|ghs_|ghu_|ghr_|github_pat_)[A-Za-z0-9_]{20,}\b"
)

# Any PEM private-key header (RSA / EC / OPENSSH / generic PKCS#8). The App's
# private key is a PEM block; finding ANY private key in a box credential file
# is a finding.
_PRIVATE_KEY_RE = re.compile(r"-----BEGIN (?:[A-Z0-9]+ )*PRIVATE KEY-----")

# Default box credential files to grep. Configurable via --env-file / the
# ``ASSERT_NO_WRITE_TOKEN_ENV_FILES`` env var so tests use temp files.
_DEFAULT_ENV_FILES: tuple[str, ...] = ("~/secrev.env", "~/orchestrator/.env")


# --------------------------------------------------------------------------- #
# Scanners. Each returns a list of human-readable finding strings.
# --------------------------------------------------------------------------- #


def scan_environ(environ: Mapping[str, str]) -> list[str]:
    """Scan a process environment for write-shaped GitHub token material.

    Flags (a) the explicit App-credential env vars, (b) any var whose *name*
    matches the GitHub-write heuristic, and (c) any var whose *value* carries a
    write-capable GitHub token prefix. Known read-only tokens are exempt.
    """
    findings: list[str] = []
    for name, value in environ.items():
        if name in _ALLOWED_TOKEN_ENV_VARS:
            continue
        if name in _FORBIDDEN_ENV_VARS:
            findings.append(
                f"environment variable {name!r} is set — the App write "
                "credential must live ONLY as an Actions secret, never on the box"
            )
            continue
        if _WRITE_TOKEN_NAME_RE.search(name):
            findings.append(
                f"environment variable {name!r} has a GitHub write-token-shaped "
                "name; the box must hold no standing write token"
            )
            continue
        if value and _WRITE_TOKEN_VALUE_RE.search(value):
            findings.append(
                f"environment variable {name!r} holds a write-capable GitHub "
                "token value (ghp_/ghs_/ghu_/ghr_/github_pat_ prefix)"
            )
    return findings


def scan_config(config: Mapping[str, object] | None) -> list[str]:
    """Scan a coordinator config mapping for write-shaped token material.

    The coordinator is environment-driven, so this is normally a thin pass over
    whatever config dict a caller hands in (string values only). It applies the
    same name/value heuristics as :func:`scan_environ`.
    """
    if not config:
        return []
    findings: list[str] = []
    for key, raw in config.items():
        name = str(key)
        if name in _ALLOWED_TOKEN_ENV_VARS:
            continue
        if name in _FORBIDDEN_ENV_VARS or _WRITE_TOKEN_NAME_RE.search(name):
            findings.append(
                f"coordinator config key {name!r} is a GitHub write-token-shaped "
                "key; the box config must hold no standing write token"
            )
            continue
        if isinstance(raw, str) and _WRITE_TOKEN_VALUE_RE.search(raw):
            findings.append(
                f"coordinator config key {name!r} holds a write-capable GitHub "
                "token value (ghp_/ghs_/ghu_/ghr_/github_pat_ prefix)"
            )
    return findings


def scan_env_file(path: Path, *, app_id: str | None = None) -> list[str]:
    """Grep one credential file for the App id and any PEM private-key header.

    A non-existent file is **not** a finding (the box legitimately may not have
    every file). An unreadable-but-present file is reported as a finding so a
    permissions mistake can't silently mask leaked material.

    When ``app_id`` is given (the configured ``AGENT_APPLY_APP_ID`` value), the
    grep also flags that literal id appearing in the file. The
    ``AGENT_APPLY_APP_ID`` / ``AGENT_APPLY_APP_PRIVATE_KEY`` *names* are always
    flagged regardless.
    """
    findings: list[str] = []
    if not path.exists():
        return findings
    try:
        text = path.read_text(encoding="utf-8", errors="replace")
    except OSError as exc:  # present but unreadable — fail loud, not silent
        return [
            f"could not read credential file {path} ({exc}); cannot prove it is clean"
        ]

    for lineno, line in enumerate(text.splitlines(), start=1):
        if APP_ID_ENV in line or APP_PRIVATE_KEY_ENV in line:
            findings.append(
                f"{path}:{lineno}: references the App credential "
                f"({APP_ID_ENV}/{APP_PRIVATE_KEY_ENV}); it must live ONLY as an "
                "Actions secret"
            )
        if app_id and app_id in line:
            findings.append(
                f"{path}:{lineno}: contains the configured App id value; the App "
                "id must not be present on the box"
            )

    if _PRIVATE_KEY_RE.search(text):
        findings.append(
            f"{path}: contains a PEM private-key block "
            "(-----BEGIN ... PRIVATE KEY-----); no private key may live on the box"
        )
    return findings


# --------------------------------------------------------------------------- #
# Orchestration.
# --------------------------------------------------------------------------- #


def _resolve_env_files(
    cli_files: Sequence[str] | None, environ: Mapping[str, str]
) -> list[Path]:
    """Resolve the credential files to grep (CLI > env var > defaults)."""
    if cli_files:
        raw = list(cli_files)
    elif environ.get("ASSERT_NO_WRITE_TOKEN_ENV_FILES"):
        raw = [
            p.strip()
            for p in environ["ASSERT_NO_WRITE_TOKEN_ENV_FILES"].split(os.pathsep)
            if p.strip()
        ]
    else:
        raw = list(_DEFAULT_ENV_FILES)
    return [Path(p).expanduser() for p in raw]


def audit(
    *,
    environ: Mapping[str, str] | None = None,
    config: Mapping[str, object] | None = None,
    env_files: Sequence[str] | None = None,
) -> list[str]:
    """Run every scanner and return the combined list of findings (empty == clean)."""
    environ = os.environ if environ is None else environ
    findings: list[str] = []
    findings += scan_environ(environ)
    findings += scan_config(config)
    app_id = environ.get(APP_ID_ENV) or None
    for path in _resolve_env_files(env_files, environ):
        findings += scan_env_file(path, app_id=app_id)
    return findings


def main(argv: Sequence[str] | None = None) -> int:
    parser = argparse.ArgumentParser(
        description=(
            "Assert no pull-requests:write / contents:write GitHub token (or the "
            "apply App's id/private key) is present on this box."
        )
    )
    parser.add_argument(
        "--env-file",
        action="append",
        dest="env_files",
        metavar="PATH",
        help=(
            "Credential file to grep for the App id + private keys (repeatable). "
            "Defaults to ~/secrev.env and ~/orchestrator/.env, or the os.pathsep-"
            "separated ASSERT_NO_WRITE_TOKEN_ENV_FILES env var."
        ),
    )
    args = parser.parse_args(argv)

    findings = audit(env_files=args.env_files)

    if findings:
        print(
            "FAIL: write-capable GitHub credential material found on the box "
            f"({len(findings)} finding(s)). The pull-requests:write App token "
            "must only ever live as an Actions secret:",
            file=sys.stderr,
        )
        for f in findings:
            print(f"  - {f}", file=sys.stderr)
        return 1

    print(
        "OK: no pull-requests:write / contents:write token, App id, or private "
        "key found in the environment, coordinator config, or credential files. "
        "The box holds no standing write token."
    )
    return 0


if __name__ == "__main__":
    raise SystemExit(main())