In order to interact with the Offective API, you or your application must authenticate.
The Offective API handles this through an API key which you can retreive from within your Offective dashboard.
The API key functions as the most important part in the authentication process. In effect, it acts as a substitute for a password.
Because of this, it is absolutely essential that you keep your API key secure. Upon generation from within Offective, the web interface will only display the token a single time in order to prevent the token from being compromised.
So, in order to authenticate you must make sure you have the API module enabled in your Offective account and you have an API key. To authenticate, Offective expects two header parameters within every request: Offective-ApiKey and Offective-Username. The username obviously is the username you login to Offective with.
An simple CURL example request can be found for every endpoint documentation on this website. The example includes the authentication headers.