#if DEBUG

var cors = new EnableCorsAttribute("*", "*", "*");
config.EnableCors(cors);

#if DEBUG

config.MapHttpAttributeRoutes();
...

public static void Register()
{
    ConfigOptions options = new ConfigOptions();

    HttpConfiguration config = ServiceConfig.Initialize(new ConfigBuilder(options));

    #if DEBUG

    var cors = new EnableCorsAttribute("*", "*", "*");
    config.EnableCors(cors);

    #endif
}

<system.webServer>
    <httpProtocol>
        <customHeaders>
            <add name="Access-Control-Allow-Origin" value="*" />
        </customHeaders>
     </httpProtocol>
     ...