JIRA allows to add optional fields called custom fields. You can choose between Standard and Advanced types while creating one. SLA PowerBox plugin extends range of Advanced type. It adds custom fields that in a way are a duplicate of standard fields (the same range of choice) except that they additionally assign permissions.
Adding a field directly to an issue
Secure custom fields can be created by JIRA Admins while being in View Issue with the Admin > Add field > Advanced option. Note, that you do not have to leave the screens when you want to configure the options for the chosen custom field.
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