Task permissions: forbid users to forward/delegate tasks to other users

Hello,

I want to implement the following scenario: users can only work on “their” tasks (assigned via candidate users or candidate groups), but not forward / delegate these tasks to other users. Therefore I have set the configuration flag:
configuration.setDefaultUserPermissionNameForTask(TASK_WORK.name());

Now the user is not able to assign other groups to a task anymore, ok so far.
However, now the user is not able anymore to unclaim his tasks: trying to unclaim a task via the tasklist (clicking the cross icon right next to his username) raises the following message:
“does not have one of the following permissions: ‘TASK_ASSIGN’ permission on resource ‘6af32bd4-7dfa-11ec-8772-005056911918’ of type ‘Task’ or ‘TASK_ASSIGN’ permission on resource ‘Rechnungseingang’ of type ‘ProcessDefinition’ or ‘UPDATE’ permission on resource ‘6af32bd4-7dfa-11ec-8772-005056911918’ of type ‘Task’ or ‘UPDATE_TASK’ permission on resource ‘Rechnungseingang’ of type ‘ProcessDefinition’”.

Which permissions do I need to set on the process or the task or which engine configuration to fulfill the requirement above: “As a user I can claim, unclaim and complete the tasks assigned to me via candidateUsers oder candidateGroups or assignee, but I am not able to forward my tasks to other persons”.