Using the Actions REST API Outside of Google Assistant?

We currently have a Google Action that requires users to log into our system and our OAuth account linking flow successfully provides an access token for authenticating with our fulfillment backend. This works great when our Action makes queries within Google Assistant.

We're also interested in using the Google Actions REST API with own custom chatbot in our web app, our iOS app, and other app platforms, but when making requests of the Google Actions API outside of Google Assistant, we keep receiving 401 authentication error responses.

Is it possible to use the Google Actions REST API outside of the Google Assistant environment? If so, then would someone be able to tell us what we're missing in our REST API calls?

As an example, based on the Google Actions REST API documentation - https://developers.google.com/assistant/actions/api - if we include our valid OAuth access token via the "Authorization: Bearer" header when making a test Google Actions REST API call via the command line:

curl -X POST "https://actions.googleapis.com/v2/projects/[OUR PROJECT ID]:matchIntents" -H "Authorization: Bearer [OUR OAUTH ACCESS TOKEN]" -H "x-goog-user-project: [OUR PROJECT ID]" -H "User-Agent: [OUR APP PLATFORM/VERSION INFO]" -H "accept: application/json" -H "Content-Type: application/json" -d "{ \"query\": \"how much money do we owe\", \"locale\": \"en-US\"}"

We always get a 401 error response, no matter how we tweak the headers:

{
  "error": {
    "code": 401,
    "message": "Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.",
    "status": "UNAUTHENTICATED"
  }
}

We've searched extensively online for any troubleshooting hints, but we have not found any answers to what we might be doing wrong here. Is there something missing from our API calls -OR- is the Google Actions REST API simply not accessible outside of the Google Assistant environment? Any help would be much appreciated.

Solution

The Actions on Google / Actions Builder platform is not designed to be used outside of the Google Assistant environment. If you want a way to programmatically match intents or call an API, you should use Dialogflow and their APIs.