Update CORS allowed headers

src/main/java/de/samply/security/SecurityConfiguration.java

@@ -123,7 +123,7 @@ CorsConfigurationSource corsConfigurationSource() {
         CorsConfiguration configuration = new CorsConfiguration();
         configuration.setAllowedOrigins(Arrays.asList(frontendConfiguration.getBaseUrl(), explorerUrl));
         configuration.setAllowedMethods(Arrays.asList("GET", "POST", "OPTIONS"));
-        configuration.setAllowedHeaders(Arrays.asList("Origin", "Content-Type", "Accept", "Authorization")); // Allow required headers
+        configuration.setAllowedHeaders(Arrays.asList(HttpHeaders.ORIGIN, HttpHeaders.CONTENT_TYPE, HttpHeaders.ACCEPT, HttpHeaders.AUTHORIZATION, "Returnaccept")); // Allow required headers
         configuration.setAllowCredentials(true); // Allow credentials
         configuration.setExposedHeaders(Arrays.asList(HttpHeaders.ACCESS_CONTROL_ALLOW_ORIGIN, HttpHeaders.ACCESS_CONTROL_ALLOW_CREDENTIALS, HttpHeaders.CONTENT_DISPOSITION)); // Expose required headers
         UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();