gh-action-pypi-publish/oidc-exchange.py

import os
import sys
from http import HTTPStatus
from pathlib import Path
from typing import NoReturn
from urllib.parse import urlparse

import id  # pylint: disable=redefined-builtin
import requests

_GITHUB_STEP_SUMMARY = Path(os.getenv("GITHUB_STEP_SUMMARY"))

# The top-level error message that gets rendered.
# This message wraps one of the other templates/messages defined below.
_ERROR_SUMMARY_MESSAGE = """
Trusted publisher (OIDC) exchange failure:

{message}

You're seeing this because the action wasn't given the inputs needed to
perform password-based or token-based authentication. If you intended to
perform one of those authentication methods instead of trusted
publishing, then you should double-check your secret configuration and variable
names.

Read more about trusted publishers at https://docs.pypi.org/trusted-publishers/
"""

# Rendered if OIDC identity token retrieval fails for any reason.
_TOKEN_RETRIEVAL_FAILED_MESSAGE = """
OIDC token retrieval failed: {identity_error}

This generally indicates a workflow configuration error, such as insufficient
permissions. Make sure that your workflow has `id-token: write` configured
at the job level, e.g.:

```yaml
permissions:
  id-token: write
```

Learn more at https://docs.github.com/en/actions/deployment/security-hardening-your-deployments/about-security-hardening-with-openid-connect#adding-permissions-settings.
"""

# Rendered if the package index refuses the given OIDC token.
_SERVER_REFUSED_TOKEN_EXCHANGE_MESSAGE = """
Token request failed: the server refused the request for the following reasons:

{reasons}
"""

# Rendered if the package index's token response isn't valid JSON.
_SERVER_TOKEN_RESPONSE_MALFORMED_JSON = """
Token request failed: the index produced an unexpected
{status_code} response.

This strongly suggests a server configuration or downtime issue; wait
a few minutes and try again.
"""

# Rendered if the package index's token response isn't a valid API token payload.
_SERVER_TOKEN_RESPONSE_MALFORMED_MESSAGE = """
Token response error: the index gave us an invalid response.

This strongly suggests a server configuration or downtime issue; wait
a few minutes and try again.
"""


def die(msg: str) -> NoReturn:
    with _GITHUB_STEP_SUMMARY.open("a", encoding="utf-8") as io:
        print(_ERROR_SUMMARY_MESSAGE.format(message=msg), file=io)

    print(f"::error::OIDC exchange failure: {msg}", file=sys.stderr)
    sys.exit(1)


def debug(msg: str):
    print(f"::debug::{msg.title()}", file=sys.stderr)


def get_normalized_input(name: str) -> str | None:
    name = f"INPUT_{name.upper()}"
    if val := os.getenv(name):
        return val
    return os.getenv(name.replace("-", "_"))


def assert_successful_audience_call(resp: requests.Response, domain: str):
    if resp.ok:
        return

    match resp.status_code:
        case HTTPStatus.FORBIDDEN:
            # This index supports OIDC, but forbids the client from using
            # it (either because it's disabled, limited to a beta group, etc.)
            die(f"audience retrieval failed: repository at {domain} has OIDC disabled")
        case HTTPStatus.NOT_FOUND:
            # This index does not support OIDC.
            die(
                "audience retrieval failed: repository at "
                f"{domain} does not indicate OIDC support",
            )
        case other:
            status = HTTPStatus(other)
            # Unknown: the index may or may not support OIDC, but didn't respond with
            # something we expect. This can happen if the index is broken, in maintenance mode,
            # misconfigured, etc.
            die(
                "audience retrieval failed: repository at "
                f"{domain} responded with unexpected {other}: {status.phrase}",
            )


repository_url = get_normalized_input("repository-url")
repository_domain = urlparse(repository_url).netloc
token_exchange_url = f"https://{repository_domain}/_/oidc/github/mint-token"

# Indices are expected to support `https://{domain}/_/oidc/audience`,
# which tells OIDC exchange clients which audience to use.
audience_url = f"https://{repository_domain}/_/oidc/audience"
audience_resp = requests.get(audience_url)
assert_successful_audience_call(audience_resp, repository_domain)

oidc_audience = audience_resp.json()["audience"]

debug(f"selected OIDC token exchange endpoint: {token_exchange_url}")

try:
    oidc_token = id.detect_credential(audience=oidc_audience)
except id.IdentityError as identity_error:
    die(_TOKEN_RETRIEVAL_FAILED_MESSAGE.format(identity_error=identity_error))

# Now we can do the actual token exchange.
mint_token_resp = requests.post(
    token_exchange_url,
    json={"token": oidc_token},
)

try:
    mint_token_payload = mint_token_resp.json()
except requests.JSONDecodeError:
    # Token exchange failure normally produces a JSON error response, but
    # we might have hit a server error instead.
    die(
        _SERVER_TOKEN_RESPONSE_MALFORMED_JSON.format(
            status_code=mint_token_resp.status_code,
        ),
    )

# On failure, the JSON response includes the list of errors that
# occurred during minting.
if not mint_token_resp.ok:
    reasons = "\n".join(
        f"* `{error['code']}`: {error['description']}"
        for error in mint_token_payload["errors"]
    )

    die(_SERVER_REFUSED_TOKEN_EXCHANGE_MESSAGE.format(reasons=reasons))

pypi_token = mint_token_payload.get("token")
if pypi_token is None:
    die(_SERVER_TOKEN_RESPONSE_MALFORMED_MESSAGE)

# Mask the newly minted PyPI token, so that we don't accidentally leak it in logs.
print(f"::add-mask::{pypi_token}", file=sys.stderr)

# This final print will be captured by the subshell in `twine-upload.sh`.
print(pypi_token)