feat: lowercase headers to exclude in exapp proxy

Signed-off-by: Anupam Kumar <kyteinsky@gmail.com>

Author: kyteinsky

lib/Controller/ExAppProxyController.php

@@ -321,6 +321,11 @@ private function passesExAppProxyRouteAccessLevelCheck(int $accessLevel): bool {
 
 	private function buildHeadersWithExclude(array $route, array $headers): array {
 		$headersToExclude = json_decode($route['headers_to_exclude'], true);
+		if ($headersToExclude === false) {
+			$headersToExclude = [];
+		}
+		$headersToExclude = array_map('strtolower', $headersToExclude);
+
 		if (!in_array('x-origin-ip', $headersToExclude)) {
 			$headersToExclude[] = 'x-origin-ip';
 		}