如何在自托管 API 上添加此代码

根据这个问题，当在Windows服务上自行连接Web api时，我无法实现IHttp模块

有没有办法在webApi与HttpSelfHostServer一起运行时添加httpModule？

但是，我仍然需要在自托管的 Web API 中的某个位置添加此代码。我找到了这个关于如何解决这个问题的博客：http://www.silver-it.com/node/182

代码如下，但是我不能在自身托管的API上实现IhttpModule

。

public class CORSPreflightModule : IHttpModule
    {
        private const string OPTIONSMETHOD = "OPTIONS";
        private const string ORIGINHEADER = "ORIGIN";
        private const string ALLOWEDORIGIN = "https://yourspodomain.sharepoint.com";
        void IHttpModule.Dispose()
        {
        }
        void IHttpModule.Init(HttpApplication context)
        {                 
            context.PreSendRequestHeaders += (sender, e) =>
            {
                var response = context.Response;
                if (context.Request.Headers[ORIGINHEADER] == ALLOWEDORIGIN)
                {
                    response.Headers.Add("Access-Control-Allow-Methods", "GET,POST,PUT,DELETE,OPTIONS");                    
                    response.Headers.Add("Access-Control-Allow-Headers", "Content-Type");                                        
                }
                if (context.Request.HttpMethod.ToUpperInvariant() == OPTIONSMETHOD && context.Request.Headers[ORIGINHEADER] == ALLOWEDORIGIN)
                {
                    response.Headers.Clear();
                    response.Headers.Add("Access-Control-Allow-Methods", "GET,POST,PUT,DELETE,OPTIONS");
                    response.Headers.Add("Access-Control-Allow-Origin", "https://yourspodomain.sharepoint.com");
                    response.Headers.Add("Access-Control-Allow-Credentials", "true");
                    response.Headers.Add("Access-Control-Allow-Headers", "Content-Type");
                    response.Clear();
                    response.StatusCode = (int)HttpStatusCode.OK;
                }                                                             
            };
        }        
    }

我的自托管 Web API 如下所示：

程序.cs

static void Main()
{
    try
    {
        ServiceBase[] ServicesToRun;
        ServicesToRun = new ServiceBase[]
        {
            new APIServiceTest()
        };
        ServiceBase.Run(ServicesToRun);
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

class Startup
    {
        //  Hack from https://stackoverflow.com/a/17227764/19020 to load controllers in 
        //  another assembly.  Another way to do this is to create a custom assembly resolver
        //Type valuesControllerType = typeof(OWINTest.API.ValuesController);
        // This code configures Web API. The Startup class is specified as a type
        // parameter in the WebApp.Start method.
        public void Configuration(IAppBuilder appBuilder)
        {
            try
            {
                //Debugger.Launch();
                // Configure Web API for self-host. 
                HttpConfiguration config = new HttpConfiguration();
                config.MessageHandlers.Add(new CustomHeaderHandler());
                var corsAttr = new EnableCorsAttribute(System.Configuration.ConfigurationManager.AppSettings["DominioSharePoint"].ToString(), "*", "*");
                config.EnableCors(corsAttr);
                //  Enable attribute based routing
                //  http://www.asp.net/web-api/overview/web-api-routing-and-actions/attribute-routing-in-web-api-2
                config.MapHttpAttributeRoutes();
                config.Routes.MapHttpRoute(
                    name: "DefaultApi",
                    routeTemplate: "api/{controller}/{id}",
                    defaults: new { id = RouteParameter.Optional }
                );
                appBuilder.UseWebApi(config);
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }
    }

我的控制器：

 [EnableCors(origins: "https://xx.sharepoint.com", headers: "*", methods: "*")]
    public class CuentasCobroController : ApiController
    {

但是，由于它是自托管的，我无法如上所述在那里实现 IHttpModule，但我可以创建自定义处理程序，如何在自定义处理程序中从博客中实现上述代码？

public class CustomHeaderHandler : DelegatingHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
        {
            return base.SendAsync(request, cancellationToken)
                .ContinueWith((task) =>
                {
                    HttpResponseMessage response = task.Result;
                    response.Headers.Add("Access-Control-Allow-Origin", "*");
                    return response;
                });
        }
    }

问题是，如何将第一个代码集成到我的 Windows 服务的启动中？

config.MessageHandlers.Add(new CorsHeaderHandler());

public class CorsHeaderHandler : DelegatingHandler
{
    private const string OPTIONSMETHOD = "OPTIONS";
    private const string ORIGINHEADER = "ORIGIN";
    private const string ALLOWEDORIGIN = "https://yourspodomain.sharepoint.com";
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
    {
        return base.SendAsync(request, cancellationToken).ContinueWith(task =>
        {
            var allowedOrigin = request.Headers.Any(t => t.Key == ORIGINHEADER && t.Value.Contains(ALLOWEDORIGIN));
            if (allowedOrigin == false) return task.Result;
            if (request.Method == HttpMethod.Options)
            {
                var emptyResponse = new HttpResponseMessage(HttpStatusCode.OK);
                emptyResponse.Headers.Add("Access-Control-Allow-Methods", "GET,POST,PUT,DELETE,OPTIONS");
                emptyResponse.Headers.Add("Access-Control-Allow-Origin", ALLOWEDORIGIN);
                emptyResponse.Headers.Add("Access-Control-Allow-Credentials", "true");
                emptyResponse.Headers.Add("Access-Control-Allow-Headers", "Content-Type");
                return emptyResponse;
            }
            else
            {
                task.Result.Headers.Add("Access-Control-Allow-Methods", "GET,POST,PUT,DELETE,OPTIONS");
                task.Result.Headers.Add("Access-Control-Allow-Headers", "Content-Type");
                return task.Result;
            }
        });
    }
}