The action can be one of two values (no value needs to be set, but the argument must be present):
Retrieve a simple list of all the site-members.
A complex list of all the site members is returned, along with the groups on the site that each person belongs to.
A list of people that belong to at least one group on the site.
Retrieving a list of user-identifiers.
$ wget --post-data='token=Fake&users' \ http://groups.example.com/gs-site-member-list.json
Retrieving a list of profiles for the people that belong to at least one group on the site:
$ wget --post-data='token=Falke&user_groups' \ http://groups.example.com/gs-site-member-list.json