SOLR_SECURITY_ALLOWED_PROXYUSERS lists all of the users allowed to impersonate. For a user x in SOLR_SECURITY_ALLOWED_PROXYUSERS, SOLR_SECURITY_PROXYUSER_x_HOSTS list the hosts x is allowed to connect from to
impersonate, and SOLR_SECURITY_PROXYUSERS_x_GROUPS lists the groups that the users is allowed to impersonate members of. Both GROUPS and
HOSTS support the wildcard * and both GROUPS and HOSTS must be defined for a specific user.