def validate_iss(valid_iss)
      return unless valid_iss && valid_iss.length > 0

      unless valid_iss.include?(self["iss"])
        raise Sandal::ClaimError, "The issuer is invalid."
      end
    end
def validate_iss(valid_iss)
      return unless valid_iss && valid_iss.length > 0

      unless valid_iss.include?(self["iss"])
        raise Sandal::ClaimError, "The issuer is invalid."
      end
    end
Validates the issuer claim.

 @param valid_iss [Array] The valid issuers.
 @return [void].
 @raise [Sandal::ClaimError] The "iss" claim value is not a valid issuer.