Insert the groups which starts with a case insensitive keyword into the ID token with an Auth0 rule

group_filter_rule.js

function (user, context, callback) {
  const namespace = 'https://acme.com/';
  const KEY_WORD = "ruler"; // Any groups which start with Ruler is inserted.
  
  function selectGroups(group) {
    return group.toLowerCase().indexOf(KEY_WORD) === 0;
  }
  context.idToken[namespace + 'groups'] = user.groups && 
                                          user.groups.filter(selectGroups);
  callback(null, user, context);
}