Boolean mapper for getting admin-permissions in nextcloud

Getting advice
1

Hi!

I try to use keycloak for my nextcloud with oidc login app in nextcloud.

There are some oidc_login_attributes as

  'oidc_login_attributes' => array ( 
    'id' => 'preferred_username', 
    'name' => 'name', 
    'mail' => 'email', 
    //'quota' => 'ownCloudQuota', 
    'groups' => 'ownCloudGroups', 
    'is_admin' => 'ownCloudAdmin',
)

and i try to figure out, to get the “is_admin” working.
So i think, the Token Claim Name should be for example “ownCloudAdmin” and a boolean value.

But i have no idea, how to map in case from the existance of a role (for example “perm-app-nextcloud_admins”) get a true or false into the token.

I found this
https://wiki.hostsharing.net/index.php/Keycloak_installieren
but not advice how to configure the ownCloudAdmin.
And my websearch for this, is_admin and similar search-phrases did not make me any wiser… So i came back here to ask, if someone solved this before.

My setup is a keycloak with ldap as backend for users, groups and so on.
In ldap have the group perm-app-nextcloud_admins. And if a user is a member of this group, the user should get admin-permission on the nextcloud instance. It the user is not member of this group, it should be only a “normal” user.

Any ideas?

thank you

Jakob