The Dev API uses a token based authentication. You have to include the token in the header of every request, along with the email address of the user who generated the token. Each Copper user can generate API keys and can have multiple valid tokens at the same time. Admins can see all user generated tokens.
To generate an API token, in the Copper web app go to System settings > API Keys and click the 'CREATE A KEY' button. Copper allows you to label each key for its unique purpose. You'll need to generate an API key to make an API Request.