KNOX-3192: Check for HttpsURLConnection before cast (#1099)

diff --git a/gateway-provider-security-authc-remote/src/main/java/org/apache/knox/gateway/filter/RemoteAuthFilter.java b/gateway-provider-security-authc-remote/src/main/java/org/apache/knox/gateway/filter/RemoteAuthFilter.java
index 29536d3..799289c 100755
--- a/gateway-provider-security-authc-remote/src/main/java/org/apache/knox/gateway/filter/RemoteAuthFilter.java
+++ b/gateway-provider-security-authc-remote/src/main/java/org/apache/knox/gateway/filter/RemoteAuthFilter.java
@@ -279,7 +279,7 @@
     if (httpURLConnection == null) {
       URL url = new URL(remoteAuthUrl);
       connection = (HttpURLConnection) url.openConnection();
-      if (trustStore != null) {
+      if (trustStore != null && connection instanceof HttpsURLConnection) {
         try {
           ((HttpsURLConnection) connection).setSSLSocketFactory(createSSLSocketFactory(trustStore));
         } catch (Exception e) {