To get the OAuth access token, use the POST /oauth/token resource. The following example sets the API key to the client_id in the POST entity, also called the request body or payload.
POST /oauth20/token/ {client_id=a78b756bd47e258841d7f007f3f62a&grant_type=password}
To get the top-level categories, use the Categories resource. Use the access token acquired in Step 1 as the bearer token in the Authorization header. This example request overrides the default text format (XML) for the Commerce API. In the Accept header set the format to application/json.
GET https://api.digitalriver.com/v1/shoppers/me/categories HTTP/1.1Header:Accept:application/jsonAuthorization:bearer your_access_token