Validate Signature

        :param data: The Request data
        :type data: dict

        :param cert: The certificate to check signature
        :type cert: str

        :param saml_type: The target URL the user should be redirected to
        :type saml_type: string  SAMLRequest | SAMLResponse

        :param raise_exceptions: Whether to return false on failure or raise an exception
        :type raise_exceptions: Boolean

def __validate_signature(self, data, saml_type, raise_exceptions=False):
        """
        Validate Signature

        :param data: The Request data
        :type data: dict

        :param cert: The certificate to check signature
        :type cert: str

        :param saml_type: The target URL the user should be redirected to
        :type saml_type: string  SAMLRequest | SAMLResponse

        :param raise_exceptions: Whether to return false on failure or raise an exception
        :type raise_exceptions: Boolean
        """
        try:
            signature = data.get('Signature', None)
            if signature is None:
                if self.__settings.is_strict() and self.__settings.get_security_data().get('wantMessagesSigned', False):
                    raise OneLogin_Saml2_ValidationError(
                        'The %s is not signed. Rejected.' % saml_type,
                        OneLogin_Saml2_ValidationError.NO_SIGNED_MESSAGE
                    )
                return True

            idp_data = self.get_settings().get_idp_data()

            exists_x509cert = 'x509cert' in idp_data and idp_data['x509cert']
            exists_multix509sign = 'x509certMulti' in idp_data and \
                'signing' in idp_data['x509certMulti'] and \
                idp_data['x509certMulti']['signing']

            if not (exists_x509cert or exists_multix509sign):
                error_msg = 'In order to validate the sign on the %s, the x509cert of the IdP is required' % saml_type
                self.__errors.append(error_msg)
                raise OneLogin_Saml2_Error(
                    error_msg,
                    OneLogin_Saml2_Error.CERT_NOT_FOUND
                )

            sign_alg = data.get('SigAlg', OneLogin_Saml2_Constants.RSA_SHA1)
            if isinstance(sign_alg, bytes):
                sign_alg = sign_alg.decode('utf8')

            lowercase_urlencoding = False
            if 'lowercase_urlencoding' in self.__request_data.keys():
                lowercase_urlencoding = self.__request_data['lowercase_urlencoding']

            signed_query = self.__build_sign_query(data[saml_type],
                                                   data.get('RelayState', None),
                                                   sign_alg,
                                                   saml_type,
                                                   lowercase_urlencoding
                                                   )

            if exists_multix509sign:
                for cert in idp_data['x509certMulti']['signing']:
                    if OneLogin_Saml2_Utils.validate_binary_sign(signed_query,
                                                                 OneLogin_Saml2_Utils.b64decode(signature),
                                                                 cert,
                                                                 sign_alg):
                        return True
                raise OneLogin_Saml2_ValidationError(
                    'Signature validation failed. %s rejected' % saml_type,
                    OneLogin_Saml2_ValidationError.INVALID_SIGNATURE
                )
            else:
                cert = idp_data['x509cert']

                if not OneLogin_Saml2_Utils.validate_binary_sign(signed_query,
                                                                 OneLogin_Saml2_Utils.b64decode(signature),
                                                                 cert,
                                                                 sign_alg,
                                                                 self.__settings.is_debug_active()):
                    raise OneLogin_Saml2_ValidationError(
                        'Signature validation failed. %s rejected' % saml_type,
                        OneLogin_Saml2_ValidationError.INVALID_SIGNATURE
                    )
            return True
        except Exception as e:
            self.__error_reason = str(e)
            if raise_exceptions:
                raise e
            return False