refactor: Adapt service account credential exchanger to base credential exchanger interface

PiperOrigin-RevId: 772710438

src/google/adk/auth/exchanger/__init__.py

@@ -15,11 +15,9 @@
 """Credential exchanger module."""
 
 from .base_credential_exchanger import BaseCredentialExchanger
-from .credential_exchanger_registry import CredentialExchangerRegistry
 from .service_account_credential_exchanger import ServiceAccountCredentialExchanger
 
 __all__ = [
     "BaseCredentialExchanger",
-    "CredentialExchangerRegistry",
     "ServiceAccountCredentialExchanger",
 ]

src/google/adk/auth/exchanger/service_account_credential_exchanger.py

@@ -16,19 +16,22 @@
 
 from __future__ import annotations
 
+from typing import Optional
+
 import google.auth
 from google.auth.transport.requests import Request
 from google.oauth2 import service_account
+from typing_extensions import override
 
-from ..utils.feature_decorator import experimental
-from .auth_credential import AuthCredential
-from .auth_credential import AuthCredentialTypes
-from .auth_credential import HttpAuth
-from .auth_credential import HttpCredentials
+from ...utils.feature_decorator import experimental
+from ..auth_credential import AuthCredential
+from ..auth_credential import AuthCredentialTypes
+from ..auth_schemes import AuthScheme
+from .base_credential_exchanger import BaseCredentialExchanger
 
 
 @experimental
-class ServiceAccountCredentialExchanger:
+class ServiceAccountCredentialExchanger(BaseCredentialExchanger):
   """Exchanges Google Service Account credentials for an access token.
 
   Uses the default service credential if `use_default_credential = True`.
@@ -36,44 +39,56 @@ class ServiceAccountCredentialExchanger:
   credential.
   """
 
-  def __init__(self, credential: AuthCredential):
-    if credential.auth_type != AuthCredentialTypes.SERVICE_ACCOUNT:
-      raise ValueError("Credential is not a service account credential.")
-    self._credential = credential
-
-  def exchange(self) -> AuthCredential:
+  @override
+  async def exchange(
+      self,
+      auth_credential: AuthCredential,
+      auth_scheme: Optional[AuthScheme] = None,
+  ) -> AuthCredential:
     """Exchanges the service account auth credential for an access token.
 
     If the AuthCredential contains a service account credential, it will be used
     to exchange for an access token. Otherwise, if use_default_credential is True,
     the default application credential will be used for exchanging an access token.
 
+    Args:
+        auth_scheme: The authentication scheme.
+        auth_credential: The credential to exchange.
+
     Returns:
-        An AuthCredential in HTTP Bearer format, containing the access token.
+        An AuthCredential in OAUTH2 format, containing the exchanged credential JSON.
 
     Raises:
         ValueError: If service account credentials are missing or invalid.
         Exception: If credential exchange or refresh fails.
     """
-    if (
-        self._credential is None
-        or self._credential.service_account is None
-        or (
-            self._credential.service_account.service_account_credential is None
-            and not self._credential.service_account.use_default_credential
+    if auth_credential is None:
+      raise ValueError("Credential cannot be None.")
+
+    if auth_credential.auth_type != AuthCredentialTypes.SERVICE_ACCOUNT:
+      raise ValueError("Credential is not a service account credential.")
+
+    if auth_credential.service_account is None:
+      raise ValueError(
+          "Service account credentials are missing. Please provide them."
       )
+
+    if (
+        auth_credential.service_account.service_account_credential is None
+        and not auth_credential.service_account.use_default_credential
     ):
       raise ValueError(
-          "Service account credentials are missing. Please provide them, or set"
-          " `use_default_credential = True` to use application default"
-          " credential in a hosted service like Google Cloud Run."
+          "Service account credentials are invalid. Please set the"
+          " service_account_credential field or set `use_default_credential ="
+          " True` to use application default credential in a hosted service"
+          " like Google Cloud Run."
       )
 
     try:
-      if self._credential.service_account.use_default_credential:
+      if auth_credential.service_account.use_default_credential:
         credentials, _ = google.auth.default()
       else:
-        config = self._credential.service_account
+        config = auth_credential.service_account
         credentials = service_account.Credentials.from_service_account_info(
             config.service_account_credential.model_dump(), scopes=config.scopes
         )
@@ -82,11 +97,8 @@ class ServiceAccountCredentialExchanger:
       credentials.refresh(Request())
 
       return AuthCredential(
-          auth_type=AuthCredentialTypes.HTTP,
-          http=HttpAuth(
-              scheme="bearer",
-              credentials=HttpCredentials(token=credentials.token),
-          ),
+          auth_type=AuthCredentialTypes.OAUTH2,
+          google_oauth2_json=credentials.to_json(),
       )
     except Exception as e:
       raise ValueError(f"Failed to exchange service account token: {e}") from e

tests/unittests/auth/exchanger/__init__.py

@@ -0,0 +1,15 @@
+# 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.
+
+"""Tests for credential exchanger."""

tests/unittests/auth/exchanger/test_service_account_credential_exchanger.py

@@ -17,19 +17,20 @@
 from unittest.mock import MagicMock
 from unittest.mock import patch
 
+from fastapi.openapi.models import HTTPBearer
 from google.adk.auth.auth_credential import AuthCredential
 from google.adk.auth.auth_credential import AuthCredentialTypes
 from google.adk.auth.auth_credential import ServiceAccount
 from google.adk.auth.auth_credential import ServiceAccountCredential
-from google.adk.auth.service_account_credential_exchanger import ServiceAccountCredentialExchanger
+from google.adk.auth.exchanger.service_account_credential_exchanger import ServiceAccountCredentialExchanger
 import pytest
 
 
 class TestServiceAccountCredentialExchanger:
   """Test cases for ServiceAccountCredentialExchanger."""
 
-  def test_init_valid_credential(self):
-    """Test successful initialization with valid service account credential."""
+  def test_exchange_with_valid_credential(self):
+    """Test successful exchange with valid service account credential."""
     credential = AuthCredential(
         auth_type=AuthCredentialTypes.SERVICE_ACCOUNT,
         service_account=ServiceAccount(
@@ -55,26 +56,36 @@ class TestServiceAccountCredentialExchanger:
         ),
     )
 
-    exchanger = ServiceAccountCredentialExchanger(credential)
-    assert exchanger._credential == credential
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
 
-  def test_init_invalid_credential_type(self):
-    """Test initialization with invalid credential type raises ValueError."""
+    # This should not raise an exception
+    assert exchanger is not None
+
+  @pytest.mark.asyncio
+  async def test_exchange_invalid_credential_type(self):
+    """Test exchange with invalid credential type raises ValueError."""
     credential = AuthCredential(
         auth_type=AuthCredentialTypes.API_KEY,
         api_key="test-key",
     )
 
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
+
     with pytest.raises(
         ValueError, match="Credential is not a service account credential"
     ):
-      ServiceAccountCredentialExchanger(credential)
+      await exchanger.exchange(credential, auth_scheme)
 
+  @pytest.mark.asyncio
   @patch(
-      "google.adk.auth.service_account_credential_exchanger.service_account.Credentials.from_service_account_info"
+      "google.adk.auth.exchanger.service_account_credential_exchanger.service_account.Credentials.from_service_account_info"
   )
-  @patch("google.adk.auth.service_account_credential_exchanger.Request")
-  def test_exchange_with_explicit_credentials_success(
+  @patch(
+      "google.adk.auth.exchanger.service_account_credential_exchanger.Request"
+  )
+  async def test_exchange_with_explicit_credentials_success(
       self, mock_request_class, mock_from_service_account_info
   ):
     """Test successful exchange with explicit service account credentials."""
@@ -84,6 +95,9 @@ class TestServiceAccountCredentialExchanger:
 
     mock_credentials = MagicMock()
     mock_credentials.token = "mock_access_token"
+    mock_credentials.to_json.return_value = (
+        '{"token": "mock_access_token", "type": "authorized_user"}'
+    )
     mock_from_service_account_info.return_value = mock_credentials
 
     # Create test credential
@@ -113,13 +127,20 @@ class TestServiceAccountCredentialExchanger:
         ),
     )
 
-    exchanger = ServiceAccountCredentialExchanger(credential)
-    result = exchanger.exchange()
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
+    result = await exchanger.exchange(credential, auth_scheme)
 
     # Verify the result
-    assert result.auth_type == AuthCredentialTypes.HTTP
-    assert result.http.scheme == "bearer"
-    assert result.http.credentials.token == "mock_access_token"
+    assert result.auth_type == AuthCredentialTypes.OAUTH2
+    assert result.google_oauth2_json is not None
+    # Verify that google_oauth2_json contains the token
+    import json
+
+    exchanged_creds = json.loads(result.google_oauth2_json)
+    assert exchanged_creds.get(
+        "token"
+    ) == "mock_access_token" or "mock_access_token" in str(exchanged_creds)
 
     # Verify mocks were called correctly
     mock_from_service_account_info.assert_called_once_with(
@@ -128,11 +149,14 @@ class TestServiceAccountCredentialExchanger:
     )
     mock_credentials.refresh.assert_called_once_with(mock_request)
 
+  @pytest.mark.asyncio
   @patch(
-      "google.adk.auth.service_account_credential_exchanger.google.auth.default"
+      "google.adk.auth.exchanger.service_account_credential_exchanger.google.auth.default"
   )
-  @patch("google.adk.auth.service_account_credential_exchanger.Request")
-  def test_exchange_with_default_credentials_success(
+  @patch(
+      "google.adk.auth.exchanger.service_account_credential_exchanger.Request"
+  )
+  async def test_exchange_with_default_credentials_success(
       self, mock_request_class, mock_google_auth_default
   ):
     """Test successful exchange with default application credentials."""
@@ -142,6 +166,9 @@ class TestServiceAccountCredentialExchanger:
 
     mock_credentials = MagicMock()
     mock_credentials.token = "default_access_token"
+    mock_credentials.to_json.return_value = (
+        '{"token": "default_access_token", "type": "authorized_user"}'
+    )
     mock_google_auth_default.return_value = (mock_credentials, "test-project")
 
     # Create test credential with use_default_credential=True
@@ -153,33 +180,45 @@ class TestServiceAccountCredentialExchanger:
         ),
     )
 
-    exchanger = ServiceAccountCredentialExchanger(credential)
-    result = exchanger.exchange()
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
+    result = await exchanger.exchange(credential, auth_scheme)
 
     # Verify the result
-    assert result.auth_type == AuthCredentialTypes.HTTP
-    assert result.http.scheme == "bearer"
-    assert result.http.credentials.token == "default_access_token"
+    assert result.auth_type == AuthCredentialTypes.OAUTH2
+    assert result.google_oauth2_json is not None
+    # Verify that google_oauth2_json contains the token
+    import json
+
+    exchanged_creds = json.loads(result.google_oauth2_json)
+    assert exchanged_creds.get(
+        "token"
+    ) == "default_access_token" or "default_access_token" in str(
+        exchanged_creds
+    )
 
     # Verify mocks were called correctly
     mock_google_auth_default.assert_called_once()
     mock_credentials.refresh.assert_called_once_with(mock_request)
 
-  def test_exchange_missing_service_account(self):
+  @pytest.mark.asyncio
+  async def test_exchange_missing_service_account(self):
     """Test exchange fails when service_account is None."""
     credential = AuthCredential(
         auth_type=AuthCredentialTypes.SERVICE_ACCOUNT,
         service_account=None,
     )
 
-    exchanger = ServiceAccountCredentialExchanger(credential)
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
 
     with pytest.raises(
         ValueError, match="Service account credentials are missing"
     ):
-      exchanger.exchange()
+      await exchanger.exchange(credential, auth_scheme)
 
-  def test_exchange_missing_credentials_and_not_default(self):
+  @pytest.mark.asyncio
+  async def test_exchange_missing_credentials_and_not_default(self):
     """Test exchange fails when credentials are missing and use_default_credential is False."""
     credential = AuthCredential(
         auth_type=AuthCredentialTypes.SERVICE_ACCOUNT,
@@ -190,17 +229,19 @@ class TestServiceAccountCredentialExchanger:
         ),
     )
 
-    exchanger = ServiceAccountCredentialExchanger(credential)
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
 
     with pytest.raises(
-        ValueError, match="Service account credentials are missing"
+        ValueError, match="Service account credentials are invalid"
     ):
-      exchanger.exchange()
+      await exchanger.exchange(credential, auth_scheme)
 
+  @pytest.mark.asyncio
   @patch(
-      "google.adk.auth.service_account_credential_exchanger.service_account.Credentials.from_service_account_info"
+      "google.adk.auth.exchanger.service_account_credential_exchanger.service_account.Credentials.from_service_account_info"
   )
-  def test_exchange_credential_creation_failure(
+  async def test_exchange_credential_creation_failure(
       self, mock_from_service_account_info
   ):
     """Test exchange handles credential creation failure gracefully."""
@@ -234,17 +275,21 @@ class TestServiceAccountCredentialExchanger:
         ),
     )
 
-    exchanger = ServiceAccountCredentialExchanger(credential)
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
 
     with pytest.raises(
         ValueError, match="Failed to exchange service account token"
     ):
-      exchanger.exchange()
+      await exchanger.exchange(credential, auth_scheme)
 
+  @pytest.mark.asyncio
   @patch(
-      "google.adk.auth.service_account_credential_exchanger.google.auth.default"
+      "google.adk.auth.exchanger.service_account_credential_exchanger.google.auth.default"
   )
-  def test_exchange_default_credential_failure(self, mock_google_auth_default):
+  async def test_exchange_default_credential_failure(
+      self, mock_google_auth_default
+  ):
     """Test exchange handles default credential failure gracefully."""
     # Setup mock to raise exception
     mock_google_auth_default.side_effect = Exception(
@@ -260,18 +305,22 @@ class TestServiceAccountCredentialExchanger:
         ),
     )
 
-    exchanger = ServiceAccountCredentialExchanger(credential)
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
 
     with pytest.raises(
         ValueError, match="Failed to exchange service account token"
     ):
-      exchanger.exchange()
+      await exchanger.exchange(credential, auth_scheme)
 
+  @pytest.mark.asyncio
   @patch(
-      "google.adk.auth.service_account_credential_exchanger.service_account.Credentials.from_service_account_info"
+      "google.adk.auth.exchanger.service_account_credential_exchanger.service_account.Credentials.from_service_account_info"
   )
-  @patch("google.adk.auth.service_account_credential_exchanger.Request")
-  def test_exchange_refresh_failure(
+  @patch(
+      "google.adk.auth.exchanger.service_account_credential_exchanger.Request"
+  )
+  async def test_exchange_refresh_failure(
       self, mock_request_class, mock_from_service_account_info
   ):
     """Test exchange handles credential refresh failure gracefully."""
@@ -312,30 +361,73 @@ class TestServiceAccountCredentialExchanger:
         ),
     )
 
-    exchanger = ServiceAccountCredentialExchanger(credential)
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
 
     with pytest.raises(
         ValueError, match="Failed to exchange service account token"
     ):
-      exchanger.exchange()
+      await exchanger.exchange(credential, auth_scheme)
 
-  def test_exchange_none_credential_in_constructor(self):
-    """Test that passing None credential raises appropriate error during construction."""
-    # This test verifies behavior when _credential is None, though this shouldn't
-    # happen in normal usage due to constructor validation
+  @pytest.mark.asyncio
+  async def test_exchange_none_credential_in_constructor(self):
+    """Test that passing None credential raises appropriate error during exchange."""
+    # This test verifies behavior when credential is None
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
+
+    with pytest.raises(ValueError, match="Credential cannot be None"):
+      await exchanger.exchange(None, auth_scheme)
+
+  @pytest.mark.asyncio
+  @patch(
+      "google.adk.auth.exchanger.service_account_credential_exchanger.google.auth.default"
+  )
+  @patch(
+      "google.adk.auth.exchanger.service_account_credential_exchanger.Request"
+  )
+  async def test_exchange_with_service_account_no_explicit_credentials(
+      self, mock_request_class, mock_google_auth_default
+  ):
+    """Test exchange with service account that has no explicit credentials uses default."""
+    # Setup mocks
+    mock_request = MagicMock()
+    mock_request_class.return_value = mock_request
+
+    mock_credentials = MagicMock()
+    mock_credentials.token = "default_access_token"
+    mock_credentials.to_json.return_value = (
+        '{"token": "default_access_token", "type": "authorized_user"}'
+    )
+    mock_google_auth_default.return_value = (mock_credentials, "test-project")
+
+    # Create test credential with no explicit credentials but use_default_credential=True
     credential = AuthCredential(
         auth_type=AuthCredentialTypes.SERVICE_ACCOUNT,
         service_account=ServiceAccount(
+            service_account_credential=None,
             use_default_credential=True,
             scopes=["https://www.googleapis.com/auth/cloud-platform"],
         ),
     )
 
-    exchanger = ServiceAccountCredentialExchanger(credential)
-    # Manually set to None to test the validation logic
-    exchanger._credential = None
+    auth_scheme = HTTPBearer()
+    exchanger = ServiceAccountCredentialExchanger()
+    result = await exchanger.exchange(credential, auth_scheme)
 
-    with pytest.raises(
-        ValueError, match="Service account credentials are missing"
-    ):
-      exchanger.exchange()
+    # Verify the result
+    assert result.auth_type == AuthCredentialTypes.OAUTH2
+    assert result.google_oauth2_json is not None
+    # Verify that google_oauth2_json contains the token
+    import json
+
+    exchanged_creds = json.loads(result.google_oauth2_json)
+    assert exchanged_creds.get(
+        "token"
+    ) == "default_access_token" or "default_access_token" in str(
+        exchanged_creds
+    )
+
+    # Verify mocks were called correctly
+    mock_google_auth_default.assert_called_once()
+    mock_credentials.refresh.assert_called_once_with(mock_request)