This is a Development API key for the Membership Opening API Set.
These API endpoints are generally system facing actions.
Note, you must have a unique key for each application or API consumer for each client. For example, if you are making a mobile application, you must have a unique API key for iOS and a unique key for Android versions of your app. In addition, you must have unique keys for each client you are serving.
These keys must be kept private and should not be viewable in publicly accessible source code.