Can a user be registered in two different CREODIAS domains?
Briefly: it is not possible. Each user, while creating CREODIAS account is identified by his mail address given during the registration process.
The mail address is equivalent for user login in clients database. For this reason, our billing and provisioning systems won't allow duplicates for avoiding issues related to confusing the same logins with several tenants.
What is more, in this case, security system sees no difference between a main account and sub-account, which causes that user with a domain created with one login cannot be subaccount using the same mail address.
Please note that this issue takes place only on CREODIAS platform and Client Area. In Horizon Dashboard each domain can contain the same user which should log in via Keystone credentials and provide a number of the domain in the login procedure.