Google Actions for Assistant (#9632)

* http: Add headers key to json[_message]

* Add google_assistant component

This component provides API endpoints for the Actions on Google Smart
Home API to interact with Google Assistant.

* google_assistant: Re-add fan support

* google_assistant: Fix Scene handling

- The way I originally wrote the MAPPING_COMPONENT and the way it's actual
  used changed so the comment was updated to match that.
- Use const's in more places
- Handle the ActivateScene command correctly

* google_assistant: Fix flakey compare test

Was failing on 3.4.2 and 3.5, this is more correct anyway.

* google_assistant: Use volume attr for media_player

homeassistant/components/google_assistant/auth.py

@@ -0,0 +1,86 @@
+"""Google Assistant OAuth View."""
+
+import asyncio
+import logging
+
+# Typing imports
+# pylint: disable=using-constant-test,unused-import,ungrouped-imports
+# if False:
+from homeassistant.core import HomeAssistant  # NOQA
+from aiohttp.web import Request, Response  # NOQA
+from typing import Dict, Any  # NOQA
+
+from homeassistant.components.http import HomeAssistantView
+from homeassistant.const import (
+    HTTP_BAD_REQUEST,
+    HTTP_UNAUTHORIZED,
+    HTTP_MOVED_PERMANENTLY,
+)
+
+from .const import (
+    GOOGLE_ASSISTANT_API_ENDPOINT,
+    CONF_PROJECT_ID, CONF_CLIENT_ID, CONF_ACCESS_TOKEN
+)
+
+BASE_OAUTH_URL = 'https://oauth-redirect.googleusercontent.com'
+REDIRECT_TEMPLATE_URL = \
+    '{}/r/{}#access_token={}&token_type=bearer&state={}'
+
+_LOGGER = logging.getLogger(__name__)
+
+
+class GoogleAssistantAuthView(HomeAssistantView):
+    """Handle Google Actions auth requests."""
+
+    url = GOOGLE_ASSISTANT_API_ENDPOINT + '/auth'
+    name = 'api:google_assistant:auth'
+    requires_auth = False
+
+    def __init__(self, hass: HomeAssistant, cfg: Dict[str, Any]) -> None:
+        """Initialize instance of the view."""
+        super().__init__()
+
+        self.project_id = cfg.get(CONF_PROJECT_ID)
+        self.client_id = cfg.get(CONF_CLIENT_ID)
+        self.access_token = cfg.get(CONF_ACCESS_TOKEN)
+
+    @asyncio.coroutine
+    def get(self, request: Request) -> Response:
+        """Handle oauth token request."""
+        query = request.query
+        redirect_uri = query.get('redirect_uri')
+        if not redirect_uri:
+            msg = 'missing redirect_uri field'
+            _LOGGER.warning(msg)
+            return self.json_message(msg, status_code=HTTP_BAD_REQUEST)
+
+        if self.project_id not in redirect_uri:
+            msg = 'missing project_id in redirect_uri'
+            _LOGGER.warning(msg)
+            return self.json_message(msg, status_code=HTTP_BAD_REQUEST)
+
+        state = query.get('state')
+        if not state:
+            msg = 'oauth request missing state'
+            _LOGGER.warning(msg)
+            return self.json_message(msg, status_code=HTTP_BAD_REQUEST)
+
+        client_id = query.get('client_id')
+        if self.client_id != client_id:
+            msg = 'invalid client id'
+            _LOGGER.warning(msg)
+            return self.json_message(msg, status_code=HTTP_UNAUTHORIZED)
+
+        generated_url = redirect_url(self.project_id, self.access_token, state)
+
+        _LOGGER.info('user login in from Google Assistant')
+        return self.json_message(
+            'redirect success',
+            status_code=HTTP_MOVED_PERMANENTLY,
+            headers={'Location': generated_url})
+
+
+def redirect_url(project_id: str, access_token: str, state: str) -> str:
+    """Generate the redirect format for the oauth request."""
+    return REDIRECT_TEMPLATE_URL.format(BASE_OAUTH_URL, project_id,
+                                        access_token, state)