docs: Add warnings regarding consuming externally sourced credentials

google/api_core/client_options.py

@@ -69,6 +69,18 @@ class ClientOptions(object):
             quota belongs to.
         credentials_file (Optional[str]): A path to a file storing credentials.
             ``credentials_file` and ``api_key`` are mutually exclusive.
+
+            .. warning::
+                Important: If you accept a credential configuration (credential JSON/File/Stream)
+                from an external source for authentication to Google Cloud Platform, you must
+                validate it before providing it to any Google API or client library. Providing an
+                unvalidated credential configuration to Google APIs or libraries can compromise
+                the security of your systems and data. For more information, refer to
+                `Validate credential configurations from external sources`_.
+
+            .. _Validate credential configurations from external sources:
+
+            https://cloud.google.com/docs/authentication/external/externally-sourced-credentials
         scopes (Optional[Sequence[str]]): OAuth access token override scopes.
         api_key (Optional[str]): Google API key. ``credentials_file`` and
             ``api_key`` are mutually exclusive.

google/api_core/grpc_helpers.py

@@ -216,6 +216,18 @@ def _create_composite_credentials(
         credentials_file (str): A file with credentials that can be loaded with
             :func:`google.auth.load_credentials_from_file`. This argument is
             mutually exclusive with credentials.
+
+            .. warning::
+                Important: If you accept a credential configuration (credential JSON/File/Stream)
+                from an external source for authentication to Google Cloud Platform, you must
+                validate it before providing it to any Google API or client library. Providing an
+                unvalidated credential configuration to Google APIs or libraries can compromise
+                the security of your systems and data. For more information, refer to
+                `Validate credential configurations from external sources`_.
+
+            .. _Validate credential configurations from external sources:
+
+            https://cloud.google.com/docs/authentication/external/externally-sourced-credentials
         default_scopes (Sequence[str]): A optional list of scopes needed for this
             service. These are only used when credentials are not specified and
             are passed to :func:`google.auth.default`.
@@ -316,6 +328,18 @@ def create_channel(
         credentials_file (str): A file with credentials that can be loaded with
             :func:`google.auth.load_credentials_from_file`. This argument is
             mutually exclusive with credentials.
+
+            .. warning::
+                Important: If you accept a credential configuration (credential JSON/File/Stream)
+                from an external source for authentication to Google Cloud Platform, you must
+                validate it before providing it to any Google API or client library. Providing an
+                unvalidated credential configuration to Google APIs or libraries can compromise
+                the security of your systems and data. For more information, refer to
+                `Validate credential configurations from external sources`_.
+
+            .. _Validate credential configurations from external sources:
+
+            https://cloud.google.com/docs/authentication/external/externally-sourced-credentials
         quota_project_id (str): An optional project to use for billing and quota.
         default_scopes (Sequence[str]): Default scopes passed by a Google client
             library. Use 'scopes' for user-defined scopes.

google/api_core/grpc_helpers_async.py

@@ -236,6 +236,18 @@ def create_channel(
         credentials_file (str): A file with credentials that can be loaded with
             :func:`google.auth.load_credentials_from_file`. This argument is
             mutually exclusive with credentials.
+
+            .. warning::
+                Important: If you accept a credential configuration (credential JSON/File/Stream)
+                from an external source for authentication to Google Cloud Platform, you must
+                validate it before providing it to any Google API or client library. Providing an
+                unvalidated credential configuration to Google APIs or libraries can compromise
+                the security of your systems and data. For more information, refer to
+                `Validate credential configurations from external sources`_.
+
+            .. _Validate credential configurations from external sources:
+
+            https://cloud.google.com/docs/authentication/external/externally-sourced-credentials
         quota_project_id (str): An optional project to use for billing and quota.
         default_scopes (Sequence[str]): Default scopes passed by a Google client
             library. Use 'scopes' for user-defined scopes.

google/api_core/operations_v1/transports/base.py

@@ -72,6 +72,18 @@ def __init__(
             credentials_file (Optional[str]): A file with credentials that can
                 be loaded with :func:`google.auth.load_credentials_from_file`.
                 This argument is mutually exclusive with credentials.
+
+                .. warning::
+                    Important: If you accept a credential configuration (credential JSON/File/Stream)
+                    from an external source for authentication to Google Cloud Platform, you must
+                    validate it before providing it to any Google API or client library. Providing an
+                    unvalidated credential configuration to Google APIs or libraries can compromise
+                    the security of your systems and data. For more information, refer to
+                    `Validate credential configurations from external sources`_.
+
+                .. _Validate credential configurations from external sources:
+
+                https://cloud.google.com/docs/authentication/external/externally-sourced-credentials
             scopes (Optional[Sequence[str]]): A list of scopes.
             quota_project_id (Optional[str]): An optional project to use for billing
                 and quota.

google/api_core/operations_v1/transports/rest.py

@@ -94,6 +94,18 @@ def __init__(
             credentials_file (Optional[str]): A file with credentials that can
                 be loaded with :func:`google.auth.load_credentials_from_file`.
                 This argument is ignored if ``channel`` is provided.
+
+                .. warning::
+                    Important: If you accept a credential configuration (credential JSON/File/Stream)
+                    from an external source for authentication to Google Cloud Platform, you must
+                    validate it before providing it to any Google API or client library. Providing an
+                    unvalidated credential configuration to Google APIs or libraries can compromise
+                    the security of your systems and data. For more information, refer to
+                    `Validate credential configurations from external sources`_.
+
+                .. _Validate credential configurations from external sources:
+
+                https://cloud.google.com/docs/authentication/external/externally-sourced-credentials
             scopes (Optional(Sequence[str])): A list of scopes. This argument is
                 ignored if ``channel`` is provided.
             client_cert_source_for_mtls (Callable[[], Tuple[bytes, bytes]]): Client