Roles
Roles in Singularity allow you to control access and management of your server.
Roles are primarily used to control and limit resources related to server management. If you want to have a more fine-grained control on which user can access what resource, check out groups.
Users
A "normal" user of your application. Can access most of the resources but is not allowed to manage your server.
Every registered account has the USER role.
This is the standard role in Singularity.
USERs can access resources that are not dealing with server administration or security.
You can learn more about users here.
Guests
Singularity allows you to create GUEST accounts.
These accounts live only in one browser session and will be invalid as soon as the browser cache is emptied.
GUESTs don't store any authentication details. Neither email nor password.
Therefore, a GUEST cannot be reauthenticated.