users-controller.js

...

fetchMe(req, res) {
  const username = req.decoded.data;
  return models.Users
  .find({
    include: [{
      model: models.Groups,
      as: 'groups',
      required: false,
      attributes: ['id', 'name'],
      through: { attributes: [] }
    }],
    where: { username }
  })

...