Update Nest integration to support Google Nest Device Access (new API) (#41689)

Co-authored-by: Paulus Schoutsen <paulus@home-assistant.io>

homeassistant/components/nest/api.py

@@ -0,0 +1,35 @@
+"""API for Google Nest Device Access bound to Home Assistant OAuth."""
+
+from aiohttp import ClientSession
+from google.oauth2.credentials import Credentials
+from google_nest_sdm.auth import AbstractAuth
+
+from homeassistant.helpers import config_entry_oauth2_flow
+
+# See https://developers.google.com/nest/device-access/registration
+
+
+class AsyncConfigEntryAuth(AbstractAuth):
+    """Provide Google Nest Device Access authentication tied to an OAuth2 based config entry."""
+
+    def __init__(
+        self,
+        websession: ClientSession,
+        oauth_session: config_entry_oauth2_flow.OAuth2Session,
+        api_url: str,
+    ):
+        """Initialize Google Nest Device Access auth."""
+        super().__init__(websession, api_url)
+        self._oauth_session = oauth_session
+
+    async def async_get_access_token(self):
+        """Return a valid access token."""
+        if not self._oauth_session.valid_token:
+            await self._oauth_session.async_ensure_token_valid()
+
+        return self._oauth_session.token["access_token"]
+
+    async def async_get_creds(self):
+        """Return a minimal OAuth credential."""
+        token = await self.async_get_access_token()
+        return Credentials(token=token)