def validate_aud(valid_aud)
      return unless valid_aud && valid_aud.length > 0

      aud = self["aud"]
      aud = [aud] unless aud.is_a?(Array)
      unless (aud & valid_aud).length > 0
        raise Sandal::ClaimError, "The audence is invalid."
      end
    end
def validate_aud(valid_aud)
      return unless valid_aud && valid_aud.length > 0

      aud = self["aud"]
      aud = [aud] unless aud.is_a?(Array)
      unless (aud & valid_aud).length > 0
        raise Sandal::ClaimError, "The audence is invalid."
      end
    end
Validates the audience claim.

 @param valid_aud [Array] The valid audiences.
 @return [void].
 @raise [Sandal::ClaimError] The "aud" claim value does not contain a valid
   audience.