Organisations
An organisation - a tenant - is who somebody is working as. It is the scope roles live in: groups belong to an organisation, and a session with no active organisation holds no roles.
Every installation owns one from its first start, and one is often all it will ever need.
Switching back to single deletes nothing: the other organisations simply stop being served, and the one that is served is the oldest.
Members
A membership is one person in one organisation, typed ADMIN or USER, and enabled or not. That is the whole enumeration - there is no OWNER membership.
Ownership is a property of the organisation, not a membership: an organisation always has an owner, the owner can be transferred, and the owner does not have to be a member. Someone who creates an organisation owns it.
An ADMIN membership, or being the owner, is what lets a person administer that organisation from the console: the organisation itself, its members, its groups, its group rules, resetting a member's password, reading a member's sign-in history. It grants nothing outside that organisation, and in particular not the global role catalogue.
A person can also leave the organisation they are in, from their profile: Leave this organisation, beside its name, then a confirmation saying that only an administrator can add them back. The membership goes, the session stops carrying the organisation at once, and the line member.leave lands in the organisation's audit trail. Multi-organisation installations only: a single one has nothing to leave.

The choice at sign-in
Once the first factor and the second factor are done:
| Memberships | What happens |
|---|---|
| none | the session is issued with no organisation. Someone who administers nothing lands in /account-pending, the waiting room |
| one | it is stamped on the session, silently |
| several | they choose, on /select-tenant |
Only enabled memberships of enabled organisations count.
A session that has no organisation and whose owner later gains exactly one membership adopts it on the next request - being added to an organisation takes effect without signing out.
Changing organisation afterwards is done from the user button, and re-runs the group step: a new organisation may have a different group mode and different groups.
Working hours
An organisation can restrict when its people may come in: weekdays, time ranges, a start and end date, in a named timezone.
The window is resolved from the narrowest level that says something: the membership, then the organisation, then the installation. When the organisation's window is the one that applies, the membership's start and end dates are still layered on top of it. The default opens every day, around the clock.
Refusing on hours says so plainly - it never looks like a wrong password.
What an organisation can override
| Setting | Levels, narrowest first | Editable where |
|---|---|---|
| Session lifetime | membership, organisation, installation | installation in the console; the two others through the admin API |
| Working hours | membership, organisation, installation | organisation in the console |
| Group mode | organisation only | the organisation's screen |
| Two-factor | account, then installation | both in the console |
Two-factor deliberately has no organisation level: the second factor is asked before the organisation is known, so a rule per organisation could not be read in time.
Everything else - the password policy, the throttle, passkeys, the theme, the languages, the relay - is installation-wide.
Isolation
Every request carries the organisation it is being made in, and that is what route rules, endpoint rules and the identity forwarded upstream are all answered against. Your service receives the organisation as a fact about the caller rather than as something the caller asked for.
One thing to know: disabling an organisation, or a membership, does not end the sessions already working there. It stops new sign-ins from adopting it, but a session that already carries that organisation keeps it, and keeps its roles in it, until the session expires.
What does take effect at once is removing somebody from a group: their roles are recomputed on the next request. So the quickest way to take access away immediately is to empty the groups, not to disable the membership.