addIdentity method
Links an OIDC identity with subject to userId and returns its ID.
Implementation
String addIdentity(String userId, {required String subject}) {
final id = nextId();
people[userId]!.identities[id] = {
'id': id,
'provider_id': localProviderId,
'provider_kind': 'oidc',
'subject': subject,
'issuer': 'https://login.example.com',
'linked_at': stamp(),
};
return id;
}