code: function createToken(username, done) {
    return getUser(username, function(getUserErr, user) {
      if (getUserErr) {
        return done(getUserErr);
      }
  
      if (!user) {
        return done(new Error(`user '${username}' not found`));
      }
  
      const token = uuid.v4();
  
      return hashToken(token, function(cryptErr, hash) {
        if (cryptErr) {
          return done(cryptErr);
        }
  
        return getModels(function(m) {
          m.collections.token.create({
            uuid: hash,
            owner: user.id,
          }, function(createTokenErr) {
            if (createTokenErr) {
              return done(createTokenErr);
            }
  
            return done(null, token);
          }); // m.collections.token.create
        }); // getModels
      }); // hashToken
    }); // getUser
  }
docs: Create a token for a user. A token is simply a v4 uuid.
  
  @param {String} username
  @param {Function} done - done(err, token)