feat(toolbox_core): add helper methods for retrieving ID tokens

packages/toolbox-core/src/toolbox_core/toolbox_auth_methods.py

@@ -0,0 +1,72 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# The tokens obtained by these functions are formatted as "Bearer" tokens
+# and are intended to be passed in the "Authorization" header of HTTP requests.
+#
+# Example User Experience:
+# from toolbox_core import toolbox_auth_methods
+#
+# auth_token_provider = toolbox_auth_methods.aget_google_id_token
+# toolbox = ToolboxClient(
+#     URL,
+#     client_headers={"Authorization": auth_token_provider},
+# )
+# tools = await toolbox.load_toolset()
+
+
+from functools import partial
+
+import google.auth
+from google.auth._credentials_async import Credentials
+from google.auth._default_async import default_async
+from google.auth.transport import _aiohttp_requests
+from google.auth.transport.requests import AuthorizedSession, Request
+
+
+async def aget_google_id_token():
+    """
+    Asynchronously fetches a Google ID token.
+
+    The token is formatted as a 'Bearer' token string and is suitable for use
+    in an HTTP Authorization header. This function uses Application Default
+    Credentials.
+
+    Returns:
+        A string in the format "Bearer <google_id_token>".
+    """
+    creds, _ = default_async()
+    await creds.refresh(_aiohttp_requests.Request())
+    creds.before_request = partial(Credentials.before_request, creds)
+    token = creds.id_token
+    return f"Bearer {token}"
+
+
+def get_google_id_token():
+    """
+    Synchronously fetches a Google ID token.
+
+    The token is formatted as a 'Bearer' token string and is suitable for use
+    in an HTTP Authorization header. This function uses Application Default
+    Credentials.
+
+    Returns:
+        A string in the format "Bearer <google_id_token>".
+    """
+    credentials, _ = google.auth.default()
+    session = AuthorizedSession(credentials)
+    request = Request(session)
+    credentials.refresh(request)
+    token = credentials.id_token
+    return f"Bearer {token}"