Helix's REST API requires authentication via the Authorization header. The format of this header is HTTP Basic Authentication. This consists of the following:

API Key (string)
Secret (string)

The API key in HTTP Basic Authentication terms is the username. The Secret in HTTP Basic Authentication terms is the password. For example, if your API Key (aka username) is "philipjfry" and your Secret (aka password) is "10.77," the authorization header will look like the following:

Authorization: Basic cGhpbGlwamZyeToxMC43Nw==