[keycloak-user] is resource owner username or userid

[uğur kolip]

Hi,
I use keycloak 2.4.0.Final with spring boot adapter, and authz-client
-authz-admin.
When i set owner , i set (getAccessToken().getPreferredUsername()) (my user
name, admin )
But when i try to get resource owner
($evaluation.getPermission().getResource().getOwner()), it returns userid
not username.
is it wrong ? or do you these purposely ?
is username unique ?  why does we use username ?

thank you for helping