Currently, it is not possible to easily determine the list of Communities and/or Collections that a user has ADMIN privileges to. This has a side-effect of not being able to determine who can manage particular Groups (as Community/Collection Admin groups need to be manageable by individuals who have Admin privileges in those Community/Collections).
This relates to https://github.com/DSpace/Rest7Contract/pull/123 and loosely to https://github.com/DSpace/DSpace/pull/2726 (as this latter PR had to add `@Ignored` annotation to some tests in order to work around this issue).
This ticket is also very similar to
DS-4504 (which is about SUBMIT privileges instead of ADMIN privileges) and likely should be solved in a similar manner.
One possible solution therefore (based on
DS-4504) is to add a plugin very similar to the current SolrServiceResourceRestrictionPlugin, that indexes which groups have Admin privileges in a given Collection/Community within the Solr record of each Collection/Community. This will provide improved performance in looking up Collection/Community Admin permissions, as you can search Solr for all Collections/Communities that provide one of your Groups with ADMIN privileges.