ASP.NET Custom WebHook implementation

Question

I want to create a webhook receiver for my Smoobu account. I created a Web Api based web application and installed Microsoft.AspNet.WebHooks.Receivers.Custom package.

Key files included in the project and their content are like the following:

App_Start\WebApiConfig.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Http;

namespace SmoobuWebHook
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services

            // Web API routes
            config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );

            // Initialize Custom WebHook receiver
            config.InitializeReceiveCustomWebHooks();

        }
    }
}

Web.config

<?xml version="1.0" encoding="utf-8"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  https://go.microsoft.com/fwlink/?LinkId=301879
  -->
<configuration>
  <appSettings>
    <add key="MS_WebHookReceiverSecret_Custom" value="12345678901234567890123456789012" />
  </appSettings>
  <system.web>
    <compilation debug="true" targetFramework="4.7.2" />
    <httpRuntime targetFramework="4.7.2" />
  </system.web>
  <system.webServer>
    <handlers>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <remove name="OPTIONSVerbHandler" />
      <remove name="TRACEVerbHandler" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" type="System.Web.Handlers.TransferRequestHandler" preCondition="integratedMode,runtimeVersionv4.0" />
    </handlers>
  </system.webServer>
  <runtime>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="Newtonsoft.Json" publicKeyToken="30ad4fe6b2a6aeed" />
        <bindingRedirect oldVersion="0.0.0.0-12.0.0.0" newVersion="12.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Helpers" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="0.0.0.0-5.2.7.0" newVersion="5.2.7.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.WebPages" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="0.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Http" publicKeyToken="31bf3856ad364e35" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-5.2.7.0" newVersion="5.2.7.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Net.Http.Formatting" publicKeyToken="31bf3856ad364e35" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-5.2.7.0" newVersion="5.2.7.0" />
      </dependentAssembly>
    </assemblyBinding>
  </runtime>
  <system.codedom>
    <compilers>
      <compiler extension=".cs" language="c#;cs;csharp" warningLevel="4" compilerOptions="/langversion:7.3 /nowarn:1659;1699;1701;612;618" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.CSharpCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=3.6.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
      <compiler extension=".vb" language="vb;vbs;visualbasic;vbscript" warningLevel="4" compilerOptions="/langversion:default /nowarn:41008,40000,40008 /define:_MYTYPE=\&quot;Web\&quot; /optionInfer+" type="Microsoft.CodeDom.Providers.DotNetCompilerPlatform.VBCodeProvider, Microsoft.CodeDom.Providers.DotNetCompilerPlatform, Version=3.6.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35" />
    </compilers>
  </system.codedom>
</configuration>

Custom.cs

using Microsoft.AspNet.WebHooks;
using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using System.Web;

namespace SmoobuWebHook
{
    public class CustomWebHookHandler : WebHookHandler
    {
        public CustomWebHookHandler()
        {
            this.Receiver = CustomWebHookReceiver.ReceiverName;
        }

        public override Task ExecuteAsync(string generator, WebHookHandlerContext context)
        {
            // Get data from WebHook
            CustomNotifications data = context.GetDataOrDefault<CustomNotifications>();

            // Get data from each notification in this WebHook
            foreach (IDictionary<string, object> notification in data.Notifications)
            {
                Console.WriteLine(notification.ToString());
            }

            return Task.FromResult(true);
        }
    }
}

I've initiated an ngrok tunnel to my localhost.

I send post requests via Postman by including ms-signature key value in the header:

(I calculated the value of ms-signature (e1b85b27d6bcb05846c18e6a48f118e89f0c0587140de9fb3359f8370d0dba08) at https://xorbin.com/tools/sha256-hash-calculator)

As can be seen from the Postman screenshot, response message is "The WebHook signature provided by the 'ms-signature' header field does not match the value expected by the 'CustomWebHookReceiver' receiver. WebHook request is invalid.". Additionally webhook handler is not triggered in webhook receiver.

My questions:

1. What is wrong with the codes?
2. Is there a way to implement a webhook without SECRET? Asking this because in Smoobu documentation there is nothing about webhook secret configuration so I'm suspicious if they provide a secret in their webhook header...

Thanks in advance.

Answer 1

After spent hours on webhook implementation on .net, I've found the following 3-4 lines of code for php and worked for me:

header('Content-Type: application/json');
$request = file_get_contents('php://input');
$req_dump = print_r( $request, true );
$fp = file_put_contents( 'request.log', $req_dump );

You can process $req_dump however you like...