code: function can(rbac, action, resource, cb) {
    // check existance of permission
    rbac.getPermission(action, resource, (err, permission) => {
      if (err) {
        return cb(err);
      }
  
      if (!permission) {
        return cb(null, false);
      }
  
      // check user additional permissions
      if (indexOf(this.permissions, permission.name) !== -1) {
        return cb(null, true);
      }
  
      if (!this.role) {
        return cb(null, false);
      }
  
      // check permission inside user role
      return rbac.can(this.role, action, resource, cb);
    });
  
    return this;
  }
docs: Check if user has assigned a specific permission
  @param  {RBAC}  rbac Instance of RBAC
  @param  {String}   action  Name of action
  @param  {String}   resource  Name of resource
  @return {Boolean}