diff --git a/src/google/adk/auth/auth_handler.py b/src/google/adk/auth/auth_handler.py
index a0cabc28..1607dcad 100644
--- a/src/google/adk/auth/auth_handler.py
+++ b/src/google/adk/auth/auth_handler.py
@@ -112,7 +112,7 @@ class AuthHandler:
 
   def parse_and_store_auth_response(self, state: State) -> None:
 
-    credential_key = self.get_credential_key()
+    credential_key = "temp:" + self.auth_config.get_credential_key()
 
     state[credential_key] = self.auth_config.exchanged_auth_credential
     if not isinstance(
@@ -130,7 +130,7 @@ class AuthHandler:
       raise ValueError("auth_scheme is empty.")
 
   def get_auth_response(self, state: State) -> AuthCredential:
-    credential_key = self.get_credential_key()
+    credential_key = "temp:" + self.auth_config.get_credential_key()
     return state.get(credential_key, None)
 
   def generate_auth_request(self) -> AuthConfig:
@@ -192,29 +192,6 @@ class AuthHandler:
         exchanged_auth_credential=exchanged_credential,
     )
 
-  def get_credential_key(self) -> str:
-    """Generates a unique key for the given auth scheme and credential."""
-    auth_scheme = self.auth_config.auth_scheme
-    auth_credential = self.auth_config.raw_auth_credential
-    if auth_scheme.model_extra:
-      auth_scheme = auth_scheme.model_copy(deep=True)
-      auth_scheme.model_extra.clear()
-    scheme_name = (
-        f"{auth_scheme.type_.name}_{hash(auth_scheme.model_dump_json())}"
-        if auth_scheme
-        else ""
-    )
-    if auth_credential.model_extra:
-      auth_credential = auth_credential.model_copy(deep=True)
-      auth_credential.model_extra.clear()
-    credential_name = (
-        f"{auth_credential.auth_type.value}_{hash(auth_credential.model_dump_json())}"
-        if auth_credential
-        else ""
-    )
-
-    return f"temp:adk_{scheme_name}_{credential_name}"
-
   def generate_auth_uri(
       self,
   ) -> AuthCredential:
diff --git a/src/google/adk/auth/auth_tool.py b/src/google/adk/auth/auth_tool.py
index d5604243..a1a19ab8 100644
--- a/src/google/adk/auth/auth_tool.py
+++ b/src/google/adk/auth/auth_tool.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from __future__ import annotations
+
 from .auth_credential import AuthCredential
 from .auth_credential import BaseModelWithConfig
 from .auth_schemes import AuthScheme
@@ -43,6 +45,34 @@ class AuthConfig(BaseModelWithConfig):
   this field to guide the user through the OAuth2 flow and fill auth response in
   this field"""
 
+  def get_credential_key(self):
+    """Generates a hash key based on auth_scheme and raw_auth_credential. This
+    hash key can be used to store / retrieve exchanged_auth_credential in a
+    credentials store.
+    """
+    auth_scheme = self.auth_scheme
+
+    if auth_scheme.model_extra:
+      auth_scheme = auth_scheme.model_copy(deep=True)
+      auth_scheme.model_extra.clear()
+    scheme_name = (
+        f"{auth_scheme.type_.name}_{hash(auth_scheme.model_dump_json())}"
+        if auth_scheme
+        else ""
+    )
+
+    auth_credential = self.raw_auth_credential
+    if auth_credential.model_extra:
+      auth_credential = auth_credential.model_copy(deep=True)
+      auth_credential.model_extra.clear()
+    credential_name = (
+        f"{auth_credential.auth_type.value}_{hash(auth_credential.model_dump_json())}"
+        if auth_credential
+        else ""
+    )
+
+    return f"adk_{scheme_name}_{credential_name}"
+
 
 class AuthToolArguments(BaseModelWithConfig):
   """the arguments for the special long running function tool that is used to
diff --git a/tests/unittests/auth/test_auth_config.py b/tests/unittests/auth/test_auth_config.py
new file mode 100644
index 00000000..7a20cfc6
--- /dev/null
+++ b/tests/unittests/auth/test_auth_config.py
@@ -0,0 +1,91 @@
+# 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.
+
+from fastapi.openapi.models import OAuth2
+from fastapi.openapi.models import OAuthFlowAuthorizationCode
+from fastapi.openapi.models import OAuthFlows
+from google.adk.auth.auth_credential import AuthCredential
+from google.adk.auth.auth_credential import AuthCredentialTypes
+from google.adk.auth.auth_credential import OAuth2Auth
+from google.adk.auth.auth_tool import AuthConfig
+import pytest
+
+
+class TestAuthConfig:
+  """Tests for the AuthConfig method."""
+
+
+@pytest.fixture
+def oauth2_auth_scheme():
+  """Create an OAuth2 auth scheme for testing."""
+  # Create the OAuthFlows object first
+  flows = OAuthFlows(
+      authorizationCode=OAuthFlowAuthorizationCode(
+          authorizationUrl="https://example.com/oauth2/authorize",
+          tokenUrl="https://example.com/oauth2/token",
+          scopes={"read": "Read access", "write": "Write access"},
+      )
+  )
+
+  # Then create the OAuth2 object with the flows
+  return OAuth2(flows=flows)
+
+
+@pytest.fixture
+def oauth2_credentials():
+  """Create OAuth2 credentials for testing."""
+  return AuthCredential(
+      auth_type=AuthCredentialTypes.OAUTH2,
+      oauth2=OAuth2Auth(
+          client_id="mock_client_id",
+          client_secret="mock_client_secret",
+          redirect_uri="https://example.com/callback",
+      ),
+  )
+
+
+@pytest.fixture
+def auth_config(oauth2_auth_scheme, oauth2_credentials):
+  """Create an AuthConfig for testing."""
+  # Create a copy of the credentials for the exchanged_auth_credential
+  exchanged_credential = oauth2_credentials.model_copy(deep=True)
+
+  return AuthConfig(
+      auth_scheme=oauth2_auth_scheme,
+      raw_auth_credential=oauth2_credentials,
+      exchanged_auth_credential=exchanged_credential,
+  )
+
+
+def test_get_credential_key(auth_config):
+  """Test generating a unique credential key."""
+
+  key = auth_config.get_credential_key()
+  assert key.startswith("adk_oauth2_")
+  assert "_oauth2_" in key
+
+
+def test_get_credential_key_with_extras(auth_config):
+  """Test generating a key when model_extra exists."""
+  # Add model_extra to test cleanup
+
+  original_key = auth_config.get_credential_key()
+  key = auth_config.get_credential_key()
+
+  auth_config.auth_scheme.model_extra["extra_field"] = "value"
+  auth_config.raw_auth_credential.model_extra["extra_field"] = "value"
+
+  assert original_key == key
+  assert "extra_field" in auth_config.auth_scheme.model_extra
+  assert "extra_field" in auth_config.raw_auth_credential.model_extra
diff --git a/tests/unittests/auth/test_auth_handler.py b/tests/unittests/auth/test_auth_handler.py
index bdac9892..c717682a 100644
--- a/tests/unittests/auth/test_auth_handler.py
+++ b/tests/unittests/auth/test_auth_handler.py
@@ -209,31 +209,6 @@ class TestAuthHandlerInit:
     assert handler.auth_config == auth_config
 
 
-class TestGetCredentialKey:
-  """Tests for the get_credential_key method."""
-
-  def test_get_credential_key(self, auth_config):
-    """Test generating a unique credential key."""
-    handler = AuthHandler(auth_config)
-    key = handler.get_credential_key()
-    assert key.startswith("temp:adk_oauth2_")
-    assert "_oauth2_" in key
-
-  def test_get_credential_key_with_extras(self, auth_config):
-    """Test generating a key when model_extra exists."""
-    # Add model_extra to test cleanup
-
-    original_key = AuthHandler(auth_config).get_credential_key()
-    key = AuthHandler(auth_config).get_credential_key()
-
-    auth_config.auth_scheme.model_extra["extra_field"] = "value"
-    auth_config.raw_auth_credential.model_extra["extra_field"] = "value"
-
-    assert original_key == key
-    assert "extra_field" in auth_config.auth_scheme.model_extra
-    assert "extra_field" in auth_config.raw_auth_credential.model_extra
-
-
 class TestGenerateAuthUri:
   """Tests for the generate_auth_uri method."""
 
@@ -412,8 +387,8 @@ class TestGetAuthResponse:
     state = MockState()
 
     # Store a credential in the state
-    credential_key = handler.get_credential_key()
-    state[credential_key] = oauth2_credentials_with_auth_uri
+    credential_key = auth_config.get_credential_key()
+    state["temp:" + credential_key] = oauth2_credentials_with_auth_uri
 
     result = handler.get_auth_response(state)
     assert result == oauth2_credentials_with_auth_uri
@@ -443,8 +418,10 @@ class TestParseAndStoreAuthResponse:
 
     handler.parse_and_store_auth_response(state)
 
-    credential_key = handler.get_credential_key()
-    assert state[credential_key] == auth_config.exchanged_auth_credential
+    credential_key = auth_config.get_credential_key()
+    assert (
+        state["temp:" + credential_key] == auth_config.exchanged_auth_credential
+    )
 
   @patch("google.adk.auth.auth_handler.AuthHandler.exchange_auth_token")
   def test_oauth_scheme(self, mock_exchange_token, auth_config_with_exchanged):
@@ -459,8 +436,8 @@ class TestParseAndStoreAuthResponse:
 
     handler.parse_and_store_auth_response(state)
 
-    credential_key = handler.get_credential_key()
-    assert state[credential_key] == mock_exchange_token.return_value
+    credential_key = auth_config_with_exchanged.get_credential_key()
+    assert state["temp:" + credential_key] == mock_exchange_token.return_value
     assert mock_exchange_token.called