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It is needed to add usernames that are the same with yours domain usernames. Then, you have to add a password. (In a future release this won't be required, so it is recommended until then, You don't need to add a strong password )on our latest releases.
Then you could add as many users you like to.
Finally, when you try to login :
You just have to click on SSO enable SSO login and then click the button login.