fix: fix fetch_id_token credential lookup order to match adc (#748)
* fix: fix fetch_id_token credential lookup order to match adc
* fix tests
* fix linter
* update
* update
* add comments
diff --git a/google/oauth2/id_token.py b/google/oauth2/id_token.py
index 5fbb6a1..540ccd1 100644
--- a/google/oauth2/id_token.py
+++ b/google/oauth2/id_token.py
@@ -179,13 +179,14 @@
def fetch_id_token(request, audience):
"""Fetch the ID Token from the current environment.
- This function acquires ID token from the environment in the following order:
+ This function acquires ID token from the environment in the following order.
+ See https://google.aip.dev/auth/4110.
- 1. If the application is running in Compute Engine, App Engine or Cloud Run,
- then the ID token are obtained from the metadata server.
- 2. If the environment variable ``GOOGLE_APPLICATION_CREDENTIALS`` is set
+ 1. If the environment variable ``GOOGLE_APPLICATION_CREDENTIALS`` is set
to the path of a valid service account JSON file, then ID token is
acquired using this service account credentials.
+ 2. If the application is running in Compute Engine, App Engine or Cloud Run,
+ then the ID token are obtained from the metadata server.
3. If metadata server doesn't exist and no valid service account credentials
are found, :class:`~google.auth.exceptions.DefaultCredentialsError` will
be raised.
@@ -213,51 +214,51 @@
If metadata server doesn't exist and no valid service account
credentials are found.
"""
- # 1. First try to fetch ID token from metada server if it exists. The code
- # works for GAE and Cloud Run metadata server as well.
- try:
- from google.auth import compute_engine
-
- credentials = compute_engine.IDTokenCredentials(
- request, audience, use_metadata_identity_endpoint=True
- )
- credentials.refresh(request)
- return credentials.token
- except (ImportError, exceptions.TransportError, exceptions.RefreshError):
- pass
-
- # 2. Try to use service account credentials to get ID token.
-
- # Try to get credentials from the GOOGLE_APPLICATION_CREDENTIALS environment
+ # 1. Try to get credentials from the GOOGLE_APPLICATION_CREDENTIALS environment
# variable.
credentials_filename = os.environ.get(environment_vars.CREDENTIALS)
- if not (
- credentials_filename
- and os.path.exists(credentials_filename)
- and os.path.isfile(credentials_filename)
- ):
- raise exceptions.DefaultCredentialsError(
- "Neither metadata server or valid service account credentials are found."
- )
+ if credentials_filename:
+ if not (
+ os.path.exists(credentials_filename)
+ and os.path.isfile(credentials_filename)
+ ):
+ raise exceptions.DefaultCredentialsError(
+ "GOOGLE_APPLICATION_CREDENTIALS path is either not found or invalid."
+ )
+ try:
+ with open(credentials_filename, "r") as f:
+ from google.oauth2 import service_account
+
+ info = json.load(f)
+ if info.get("type") == "service_account":
+ credentials = service_account.IDTokenCredentials.from_service_account_info(
+ info, target_audience=audience
+ )
+ credentials.refresh(request)
+ return credentials.token
+ except ValueError as caught_exc:
+ new_exc = exceptions.DefaultCredentialsError(
+ "GOOGLE_APPLICATION_CREDENTIALS is not valid service account credentials.",
+ caught_exc,
+ )
+ six.raise_from(new_exc, caught_exc)
+
+ # 2. Try to fetch ID token from metada server if it exists. The code works for GAE and
+ # Cloud Run metadata server as well.
try:
- with open(credentials_filename, "r") as f:
- info = json.load(f)
- credentials_content = (
- (info.get("type") == "service_account") and info or None
+ from google.auth import compute_engine
+ from google.auth.compute_engine import _metadata
+
+ if _metadata.ping(request):
+ credentials = compute_engine.IDTokenCredentials(
+ request, audience, use_metadata_identity_endpoint=True
)
+ credentials.refresh(request)
+ return credentials.token
+ except (ImportError, exceptions.TransportError):
+ pass
- from google.oauth2 import service_account
-
- credentials = service_account.IDTokenCredentials.from_service_account_info(
- credentials_content, target_audience=audience
- )
- except ValueError as caught_exc:
- new_exc = exceptions.DefaultCredentialsError(
- "Neither metadata server or valid service account credentials are found.",
- caught_exc,
- )
- six.raise_from(new_exc, caught_exc)
-
- credentials.refresh(request)
- return credentials.token
+ raise exceptions.DefaultCredentialsError(
+ "Neither metadata server or valid service account credentials are found."
+ )