Actually, it looks like you don't need full-blown OAuth at all in this case. You can use Web Request action to make first POST request to the oauth/token endpoint, then use Return response body as action result option, parse received body as JSON and pick access_token field. I can't find any documentation regarding this Telematics service, but if this is in some way compliant with OAuth, you then should use the value of this access token in subsequent actions.