Message Interceptor in Web API

Track the pipeline process, wherein we can also validate or intercept the incoming API request. Microsoft had given us some of classes using that we can override the API Pipeline. In this example, I will implement DelegatingHandler

Here just creating a class “SecurityMessageHandler” which is inherited from “DelegatingHandler”

 Class Declaration

public class SecurityMessageHandler:DelegatingHandler

    {

    

        public SecurityMessageHandler()

        {

          

        }

       

        protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)

        {

            IEnumerable<string> headerValues;

            var tokenHeader = string.Empty;

            if (request.Headers.TryGetValues("Authorization", out headerValues))

            {

                tokenHeader = headerValues.FirstOrDefault();

            }

            if (!request.RequestUri.AbsolutePath.StartsWith("/api/"))

            {

                return await base.SendAsync(request, cancellationToken);

            }

         

            if (string.IsNullOrWhiteSpace(tokenHeader))

            {

                if (request.RequestUri.AbsolutePath.Contains("api/auth/"))

                {

                    return await base.SendAsync(request, cancellationToken);

                }

                else

                {

                    return await SendError("Wrong API Key", HttpStatusCode.Forbidden);

                }

            }

          

            return await base.SendAsync(request, cancellationToken);

        }

        private Task<HttpResponseMessage> SendError(string error, HttpStatusCode code)

        {

            var response = new HttpResponseMessage();

            response.Content = new StringContent(error);

            response.StatusCode = code;

            return Task<HttpResponseMessage>.Factory.StartNew(() => response);

        }

    }

Register the Handler

In given file location

app_start\webapiconfig.cs

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

Now under the module “SendAsync”

We can track or validate the incoming API with different process

if (!request.RequestUri.AbsolutePath.StartsWith("/api/"))

   {

     return await base.SendAsync(request, cancellationToken);

   }

Earlier we were using

base.SendAsync(request, cancellationToken).ContinueWith( (task) => 

                {

                     var response = task.Result;

                     response.Headers.Add("X-Custom-Header", "Custom-Header.");

                     return response;

                     } );

Note:  .ContinueWith from C#5 onwards, eased with using “async” and “await” see in above code