To send API-Requests you need to have an API-Key.
An API key can currently be created only by your ERP-Administrator.
To authenticate with the API you just have to append the API key as GET parameter to your request URL.
Please note that through authentication with the API key you get the same rights as the user, the API-Key is assigned to.
If you want to grant restricted access to the API please create a new user.
To retrieve the information of the user of your API-Key please use the users endpoint.