Passbolt proposes two system roles "admin" and "user". This system is the first line of the authorization mechanism performing checks directly for each user's actions.
In a nutshell, an administrator manages the instance. In practice it means that they can manage organization-wide settings such as the content of the email notifications or which multiple factor authentication provider is enabled. Another responsibility is to create or delete users, manage groups and group managers, perform synchronization with a user directory, etc.
Each group must have at least one group manager in charge of adding and removing group members. The administrators can appoint themselves as group administrator or appoint a regular user.
fig. Groups workflow
Due to the nature of the encryption in passbolt, only someone with access to the secrets of a given group can add a member to that group (as they need to be able to decrypt and encrypt the secret for the new member).