The API does not require that the logged in user must be a “Catalog Administrator”.
Any level of user can log in using the API, but the functions available to that user will limited by their access level. Most of what an Administrator can do can also be accomplished by a user of Publisher level.
For example: All users have the ability to use the DownloadPreviews method, but you will have to be an Administrator, Publisher, or Editor to be able to download the Original file.
A breakdown of the different UserPermissions and who can use them can be found here: User Permssions