There are 2 authentication methods for the API: HMAC Authentication and OAuth Token authentication. The easiest way to authenticate is using OAuth Token authentication. Upon requesting a token you will get back a json response with a access_token that will be used going forward. Here is a quick example that shows how to request a token using curl:

curl -d "grant_type=password&username=YOUR_EMAIL&password=YOUR_PASSWORD" -X POST

The email address and password need to be url encoded prior to the string construction to allow any special characters that may be present in your password. Any future requests to the API will need to include the following header:

Authorization: Bearer access_token

To request a new Token use the refresh_token from your original Token response as follows:

curl -d "grant_type=refresh_token&refresh_token=REFRESH_TOKEN" -X POST