Once a minimum of one tenant has been created, you create users for the tenant. Every S3 user has a unique pair of access and private keys, both of which are required to provision buckets and read/write data to buckets.
You can create a new Object Tier user which is associated with a single tenant. Users cannot be members of multiple tenants and must be unique within the associated tenant. You can use the same username across multiple tenants, with each user provided with a unique set of access keys.