Access to the API is limited to users in a group that contains the 'web service access' permission. Also, depending on the type of project you are doing, you can use Oauth 2 (OAuth 2 Authentication | Adobe Developer Connection ) to limit the scope of what users can do with your project.

'Permissions (Read) - Web Services' and 'Permissions (Write) - Web Services' actually refer to the ability to run certain API requests. For example, if you were to run Permissions.SaveGroup (SaveGroup | Adobe Developer Connection ), you would need 'Permissions (Write) - Web Services'. To run somethi...