In order for your realm to identify a user from a trusted realm, you must specify a unique identifier that your realm can recognize. This identifier can be the user’s domain name or e-mail address. The identifier must be unique among the trusted realms.
For example, John Smith from Realm A is jsmith in his local realm. When jsmith attempts to authenticate on your realm, your realm does not know jsmith or which realm he comes from. If you define Realm A as yourcompany.com, jsmith is identified within your realm as firstname.lastname@example.org. You can define multiple identifiers for a trusted realm.
Select the trusted realm that you want to edit.
From the context menu, click Edit.
In the Trusted User Name Identifier field under username@, specify a unique domain name that your realm can recognize.
You can add multiple domain names for a trusted realm.