SimpleSAML_Configuration::getValueValidate PHP Method

    public function getValueValidate($name, $allowedValues, $default = self::REQUIRED_OPTION)
    {
        assert('is_string($name)');
        assert('is_array($allowedValues)');
        $ret = $this->getValue($name, $default);
        if ($ret === $default) {
            // the option wasn't found, or it matches the default value. In any case, return this value
            return $ret;
        }
        if (!in_array($ret, $allowedValues, true)) {
            $strValues = array();
            foreach ($allowedValues as $av) {
                $strValues[] = var_export($av, true);
            }
            $strValues = implode(', ', $strValues);
            throw new Exception($this->location . ': Invalid value given for the option ' . var_export($name, true) . '. It should have one of the following values: ' . $strValues . '; but it had the following value: ' . var_export($ret, true));
        }
        return $ret;
    }

 /**
  * Build an authentication request based on information in the metadata.
  *
  * @param SimpleSAML_Configuration $spMetadata  The metadata of the service provider.
  * @param SimpleSAML_Configuration $idpMetadata  The metadata of the identity provider.
  */
 public static function buildAuthnRequest(SimpleSAML_Configuration $spMetadata, SimpleSAML_Configuration $idpMetadata)
 {
     $ar = new \SAML2\AuthnRequest();
     // get the NameIDPolicy to apply. IdP metadata has precedence.
     $nameIdPolicy = array();
     if ($idpMetadata->hasValue('NameIDPolicy')) {
         $nameIdPolicy = $idpMetadata->getValue('NameIDPolicy');
     } elseif ($spMetadata->hasValue('NameIDPolicy')) {
         $nameIdPolicy = $spMetadata->getValue('NameIDPolicy');
     }
     if (!is_array($nameIdPolicy)) {
         // handle old configurations where 'NameIDPolicy' was used to specify just the format
         $nameIdPolicy = array('Format' => $nameIdPolicy);
     }
     $nameIdPolicy_cf = SimpleSAML_Configuration::loadFromArray($nameIdPolicy);
     $policy = array('Format' => $nameIdPolicy_cf->getString('Format', \SAML2\Constants::NAMEID_TRANSIENT), 'AllowCreate' => $nameIdPolicy_cf->getBoolean('AllowCreate', true));
     $spNameQualifier = $nameIdPolicy_cf->getString('SPNameQualifier', false);
     if ($spNameQualifier !== false) {
         $policy['SPNameQualifier'] = $spNameQualifier;
     }
     $ar->setNameIdPolicy($policy);
     $ar->setForceAuthn($spMetadata->getBoolean('ForceAuthn', FALSE));
     $ar->setIsPassive($spMetadata->getBoolean('IsPassive', FALSE));
     $protbind = $spMetadata->getValueValidate('ProtocolBinding', array(\SAML2\Constants::BINDING_HTTP_POST, \SAML2\Constants::BINDING_HOK_SSO, \SAML2\Constants::BINDING_HTTP_ARTIFACT, \SAML2\Constants::BINDING_HTTP_REDIRECT), \SAML2\Constants::BINDING_HTTP_POST);
     /* Shoaib - setting the appropriate binding based on parameter in sp-metadata defaults to HTTP_POST */
     $ar->setProtocolBinding($protbind);
     $ar->setIssuer($spMetadata->getString('entityid'));
     $ar->setAssertionConsumerServiceIndex($spMetadata->getInteger('AssertionConsumerServiceIndex', NULL));
     $ar->setAttributeConsumingServiceIndex($spMetadata->getInteger('AttributeConsumingServiceIndex', NULL));
     if ($spMetadata->hasValue('AuthnContextClassRef')) {
         $accr = $spMetadata->getArrayizeString('AuthnContextClassRef');
         $comp = $spMetadata->getValueValidate('AuthnContextComparison', array(\SAML2\Constants::COMPARISON_EXACT, \SAML2\Constants::COMPARISON_MINIMUM, \SAML2\Constants::COMPARISON_MAXIMUM, \SAML2\Constants::COMPARISON_BETTER), \SAML2\Constants::COMPARISON_EXACT);
         $ar->setRequestedAuthnContext(array('AuthnContextClassRef' => $accr, 'Comparison' => $comp));
     }
     self::addRedirectSign($spMetadata, $idpMetadata, $ar);
     return $ar;
 }