Update autodiscover-json.php

HTTP_HOST is okay.
Syntax for consistency. :-)

data/web/autodiscover-json.php

@@ -8,16 +8,14 @@ if(file_exists('inc/vars.local.inc.php')) {
 $autodiscover_config = array_merge($default_autodiscover_config, $autodiscover_config);
 
 header('Content-type: application/json');
-
-$domain_dot = strpos($_SERVER['HTTP_HOST'], '.');
-$domain = substr($_SERVER['HTTP_HOST'], $domain_dot+1);
-
 if ($_GET['Protocol'] == 'ActiveSync') {
   echo '{"Protocol":"ActiveSync","Url":"' . $autodiscover_config['activesync']['url'] . '"}';
-} elseif ($_GET['Protocol'] == 'AutodiscoverV1') {
-  echo '{"Protocol":"AutodiscoverV1","Url":"https://autodiscover.' . $domain . '/autodiscover/autodiscover.xml"}';
-} else {
+}
+elseif ($_GET['Protocol'] == 'AutodiscoverV1') {
+  echo '{"Protocol":"AutodiscoverV1","Url":"https://' . $_SERVER['HTTP_HOST'] . '/autodiscover/autodiscover.xml"}';
+}
+else {
   http_response_code(400);
   echo '{"ErrorCode":"InvalidProtocol","ErrorMessage":"The given protocol value \u0027' . $_GET['Protocol'] . '\u0027 is invalid. Supported values are \u0027ActiveSync,AutodiscoverV1\u0027"}';
 }
-?>
+?>