adds CorsHeaders to allow usage from javascript

Author: lkwg82

api/pom.xml

@@ -56,5 +56,10 @@
             <artifactId>undertow-core</artifactId>
             <version>2.0.27.Final</version>
         </dependency>
+        <dependency>
+            <groupId>com.stijndewitt.undertow.cors</groupId>
+            <artifactId>undertow-cors-filter</artifactId>
+            <version>0.4.0</version>
+        </dependency>
     </dependencies>
 </project>

api/src/main/java/xyz/gianlu/librespot/api/ApiServer.java

@@ -1,5 +1,7 @@
 package xyz.gianlu.librespot.api;
 
+import com.stijndewitt.undertow.cors.AllowAll;
+import com.stijndewitt.undertow.cors.Filter;
 import io.undertow.Undertow;
 import io.undertow.server.RoutingHandler;
 import org.apache.log4j.Logger;
@@ -32,7 +34,12 @@ public void start(@NotNull Session session) {
         RoutingHandler handler = new RoutingHandler();
         prepareHandlers(handler, session);
 
-        undertow = Undertow.builder().addHttpListener(port, "", handler).build();
+        Filter corsFilter = new Filter(handler);
+        corsFilter.setPolicyClass(AllowAll.class.getCanonicalName());
+        corsFilter.setPolicyParam(null);
+        corsFilter.setUrlPattern(".*");
+
+        undertow = Undertow.builder().addHttpListener(port, "", corsFilter).build();
         undertow.start();
         LOGGER.info(String.format("Server started on port %d!", port));
     }