In order to use the Vista API, you must first create an API key. This can be done in the Vista Dashboard under Accounts > API Keys.
This key is responsible for verifying your identity, please follow all security best practices around maintaining secrets. Once a key is created, it can no longer be viewed in the control panel - the first few digits are made available for tracking purposes. You can also create and delete as many API keys as you wish.
All of the client libraries accept the API key as an argument in the constructor.
vc = VistaClient('Z6Q2KfVk6T5NJ65uskrfOxRCkcrSMhxQRmbAereoxUQ2YA7J')