作为参考，如果您使用
[EnableCors()]方法拦截消息管道，将不起作用。在我的情况下，我会在路由被调用之前检查请求中的
Authorization标头并相应处理，这意味着我的请求在管道中更早地被处理，因此
[EnableCors()]没有效果。
最终我找到了一个示例
CrossDomainHandler类(感谢shaunxu的Gist)，它可以在管道中为我处理CORS，只需要添加另一个消息处理程序即可。
public class CrossDomainHandler : DelegatingHandler
{
const string Origin = "Origin";
const string AccessControlRequestMethod = "Access-Control-Request-Method";
const string AccessControlRequestHeaders = "Access-Control-Request-Headers";
const string AccessControlAllowOrigin = "Access-Control-Allow-Origin";
const string AccessControlAllowMethods = "Access-Control-Allow-Methods";
const string AccessControlAllowHeaders = "Access-Control-Allow-Headers";
protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
bool isCorsRequest = request.Headers.Contains(Origin);
bool isPreflightRequest = request.Method == HttpMethod.Options;
if (isCorsRequest)
{
if (isPreflightRequest)
{
return Task.Factory.StartNew(() =>
{
HttpResponseMessage response = new HttpResponseMessage(HttpStatusCode.OK);
response.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First());
string accessControlRequestMethod = request.Headers.GetValues(AccessControlRequestMethod).FirstOrDefault();
if (accessControlRequestMethod != null)
{
response.Headers.Add(AccessControlAllowMethods, accessControlRequestMethod);
}
string requestedHeaders = string.Join(", ", request.Headers.GetValues(AccessControlRequestHeaders));
if (!string.IsNullOrEmpty(requestedHeaders))
{
response.Headers.Add(AccessControlAllowHeaders, requestedHeaders);
}
return response;
}, cancellationToken);
}
else
{
return base.SendAsync(request, cancellationToken).ContinueWith(t =>
{
HttpResponseMessage resp = t.Result;
resp.Headers.Add(AccessControlAllowOrigin, request.Headers.GetValues(Origin).First());
return resp;
});
}
}
else
{
return base.SendAsync(request, cancellationToken);
}
}
}
要使用它，请将其添加到已注册消息处理程序的列表中。
config.MessageHandlers.Add(new CrossDomainHandler());
浏览器发出的任何预检请求都将得到处理并传递，这意味着我不需要在控制器上实现[HttpOptions] IHttpActionResult方法。
