id: add ambient detector for CircleCI

Makefile

@@ -63,8 +63,7 @@ run: $(VENV)/pyvenv.cfg
 .PHONY: lint
 lint: $(VENV)/pyvenv.cfg
 	. $(VENV_BIN)/activate && \
-		black --check $(ALL_PY_SRCS) && \
-		isort --check $(ALL_PY_SRCS) && \
+		ruff format --check $(ALL_PY_SRCS) && \
 		ruff $(ALL_PY_SRCS) && \
 		mypy $(PY_MODULE) && \
 		bandit -c pyproject.toml -r $(PY_MODULE) && \
@@ -74,8 +73,7 @@ lint: $(VENV)/pyvenv.cfg
 reformat: $(VENV)/pyvenv.cfg
 	. $(VENV_BIN)/activate && \
 		ruff --fix $(ALL_PY_SRCS) && \
-		black $(ALL_PY_SRCS) && \
-		isort $(ALL_PY_SRCS)
+		ruff format $(ALL_PY_SRCS)
 
 .PHONY: test
 test: $(VENV)/pyvenv.cfg

id/__init__.py

@@ -59,6 +59,7 @@ def detect_credential(audience: str) -> Optional[str]:
     """
     from ._internal.oidc.ambient import (
         detect_buildkite,
+        detect_circleci,
         detect_gcp,
         detect_github,
         detect_gitlab,
@@ -69,6 +70,7 @@ def detect_credential(audience: str) -> Optional[str]:
         detect_gcp,
         detect_buildkite,
         detect_gitlab,
+        detect_circleci,
     ]
     for detector in detectors:
         credential = detector(audience)

id/__main__.py

@@ -36,9 +36,7 @@ def _parser() -> argparse.ArgumentParser:
         description="a tool for generating OIDC identities",
         formatter_class=argparse.ArgumentDefaultsHelpFormatter,
     )
-    parser.add_argument(
-        "-V", "--version", action="version", version=f"%(prog)s {__version__}"
-    )
+    parser.add_argument("-V", "--version", action="version", version=f"%(prog)s {__version__}")
     parser.add_argument(
         "-v",
         "--verbose",

id/_internal/oidc/ambient.py

@@ -16,6 +16,7 @@
 Ambient OIDC credential detection.
 """
 
+import json
 import logging
 import os
 import re
@@ -31,9 +32,15 @@
 logger = logging.getLogger(__name__)
 
 _GCP_PRODUCT_NAME_FILE = "/sys/class/dmi/id/product_name"
-_GCP_TOKEN_REQUEST_URL = "http://metadata/computeMetadata/v1/instance/service-accounts/default/token"  # noqa # nosec B105
-_GCP_IDENTITY_REQUEST_URL = "http://metadata/computeMetadata/v1/instance/service-accounts/default/identity"  # noqa
-_GCP_GENERATEIDTOKEN_REQUEST_URL = "https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/{}:generateIdToken"  # noqa
+_GCP_TOKEN_REQUEST_URL = (
+    "http://metadata/computeMetadata/v1/instance/service-accounts/default/token"  # noqa # nosec B105
+)
+_GCP_IDENTITY_REQUEST_URL = (
+    "http://metadata/computeMetadata/v1/instance/service-accounts/default/identity"  # noqa
+)
+_GCP_GENERATEIDTOKEN_REQUEST_URL = (
+    "https://iamcredentials.googleapis.com/v1/projects/-/serviceAccounts/{}:generateIdToken"  # noqa
+)
 
 _env_var_regex = re.compile(r"[^A-Z0-9_]|^[^A-Z_]")
 
@@ -178,15 +185,11 @@ def detect_gcp(audience: str) -> Optional[str]:
             with open(_GCP_PRODUCT_NAME_FILE) as f:
                 name = f.read().strip()
         except OSError:
-            logger.debug(
-                "GCP: environment doesn't have GCP product name file; giving up"
-            )
+            logger.debug("GCP: environment doesn't have GCP product name file; giving up")
             return None
 
         if name not in {"Google", "Google Compute Engine"}:
-            logger.debug(
-                f"GCP: product name file exists, but product name is {name!r}; giving up"
-            )
+            logger.debug(f"GCP: product name file exists, but product name is {name!r}; giving up")
             return None
 
         logger.debug("GCP: requesting OIDC token")
@@ -292,9 +295,43 @@ def detect_gitlab(audience: str) -> Optional[str]:
     var_name = f"{sanitized_audience}_ID_TOKEN"
     token = os.getenv(var_name)
     if not token:
-        raise AmbientCredentialError(
-            f"GitLab: Environment variable {var_name} not found"
-        )
+        raise AmbientCredentialError(f"GitLab: Environment variable {var_name} not found")
 
     logger.debug(f"GitLab: Found token in environment variable {var_name}")
     return token
+
+
+def detect_circleci(audience: str) -> Optional[str]:
+    """
+    Detect and return a CircleCI ambient OIDC credential.
+
+    Returns `None` if the context is not a CircleCI environment.
+
+    Raises if the environment is GitHub Actions, but is incorrect or
+    insufficiently permissioned for an OIDC credential.
+    """
+    logger.debug("CircleCI: looking for OIDC credentials")
+
+    if not os.getenv("CIRCLECI"):
+        logger.debug("CircleCI: environment doesn't look like CircleCI; giving up")
+        return None
+
+    # Check that the circleci executable exists in the `PATH`.
+    if shutil.which("circleci") is None:
+        raise AmbientCredentialError("CircleCI: could not find `circleci` in the environment")
+
+    # See NOTE on `detect_buildkite` for why we silence these warnings.
+    payload = json.dumps({"aud": audience})
+    process = subprocess.run(  # nosec B603, B607
+        ["circleci", "run", "oidc", "get", "--claims", payload],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        text=True,
+    )
+
+    if process.returncode != 0:
+        raise AmbientCredentialError(
+            f"CircleCI: the `circleci` tool encountered an error: {process.stdout}"
+        )
+
+    return process.stdout.strip()

pyproject.toml

@@ -34,8 +34,6 @@ Source = "https://github.com/di/id"
 test = ["pytest", "pytest-cov", "pretend", "coverage[toml]"]
 lint = [
   "bandit",
-  "black",
-  "isort",
   "interrogate",
   "mypy",
   # NOTE(ww): ruff is under active development, so we pin conservatively here
@@ -45,11 +43,6 @@ lint = [
 ]
 dev = ["build", "bump >= 1.3.2", "id[test,lint]"]
 
-[tool.isort]
-multi_line_output = 3
-known_first_party = "id"
-include_trailing_comma = true
-
 [tool.interrogate]
 # don't enforce documentation coverage for packaging, testing, the virtual
 # environment, or the CLI (which is documented separately).
@@ -85,4 +78,4 @@ exclude_dirs = ["./test"]
 line-length = 100
 # TODO: Enable "UP" here once Pydantic allows us to:
 # See: https://github.com/pydantic/pydantic/issues/4146
-select = ["E", "F", "W"]
+select = ["I", "E", "F", "W"]