curl \
   -k \
   -s \
   -X POST \
   -H "Content-Type:application/json" \
   -H "Accept: application/json" \
   -d '{
        "id": "foo-group",
        "GroupID": "foo-group",
        "Description": "foo people",
        "Link": {
          "rel": "self",
          "href": "https://localhost.localdomain:8443/ca/rest/admin/groups/foo-group",
          "type": "application/xml"}
      }' \
    --user caadmin:Secret.123 \
    https://localhost.localdomain:8443/ca/rest/admin/groups/ | python -m json.tool
{
    "id": "foo-group",
    "GroupID": "foo-group",
    "Description": "foo people",
    "Link": {
        "rel": "self",
        "href": "https://localhost.localdomain:8443/ca/rest/admin/groups/foo-group",
        "type": "application/xml"
    }
}