You can manage user access in a variety of ways. Every user can have a username/password required to access the service. This can also be integrated with your single-sign-on (SSO), which is supported at our Enterprise tier.
Some clients want a very low-friction way to grant access, and we support simply sharing the secret app links (similar to a Dropbox or Google drive secret link), so that anybody with that link will be able to access it directly. In that case, only your developers/admins would need to authenticate to manage your account, upload apps, download reports, etc. See Sharing Apps for more information.
Please see our Invite your team documentation on how to easily add, remove and manage your users.