feat(PassthroughParameters): Make it possible to pass through paramet…

…ers to the SAML library

OneLogin/Auth->login can accept an array of parameters to be passed through to the IdP.

This patch makes it possible to specify an array of parameters to be passed through to the IdP in config.php.

For example, you can set it like this, and if we get such a parameter in
the request to user_saml/saml/login we will pass it on to the IdP.
  'user_saml.passthrough_parameters' => ['idp_hint'],

lib/Controller/SAMLController.php

@@ -151,9 +151,18 @@ public function login(int $idp = 1): Http\RedirectResponse {
 		switch ($type) {
 			case 'saml':
 				$auth = new Auth($this->samlSettings->getOneLoginSettingsArray($idp));
+				$passthroughParams = $this->config->getSystemValue('user_saml.passthrough_parameters', []);
+				$passthroughValues = [];
+				foreach ($passthroughParams as $passthroughParam) {
+					$value = (string)$this->request->getParam($passthroughParam, '');
+					if ($value !== '') {
+						$passthroughValues[$passthroughParam] = $value;
+					}
+				}
+
 
 				$returnUrl = $originalUrl ?: $this->urlGenerator->linkToRouteAbsolute('user_saml.SAML.login');
-				$ssoUrl = $auth->login($returnUrl, [], false, false, true);
+				$ssoUrl = $auth->login($returnUrl, $passthroughValues, false, false, true);
 				$response = new Http\RedirectResponse($ssoUrl);
 
 				// Small hack to make user_saml work with the loginflows