Receiving real-time webhooks with an Azure Function

What is a webhook? Ask Google :) 😅

This is my experience building an Azure Function HTTP trigger to receive events from the SkyBox API webhook.

Business requirement: real-time integration of invoices with the SkyBox API webhook. Whenever SkyBox has a new or updated invoice, their service sends the JSON message to my API.

Solution

Step 1: Build a C# HTTP trigger function and deploy it to Azure Functions

Depending on the business requirement, you can add more in your own code.

Step 2: Add a subscription

Send a POST to https://skybox.vividseats.com/services/webhooks:

{
  "topic": "INVOICE",
  "url": "https://<your-function-app>.azurewebsites.net/api/SkyboxReceiveInvoice?code=<function-key>",
  "headers": "Bearer: <token>",
  "secret": "<your-secret-key>"
}

Then open the Azure Function’s Monitor tab to see the messages coming in.

Note: checking the signature

The secret is used to sign the message. Here is the code.

Create the key:

byte[] key = Encoding.ASCII.GetBytes("<your-secret-key>");

Encode the payload to compute the MAC to check against:

public static string Encode(string input, byte[] key)
{
    HMACSHA1 myhmacsha1 = new HMACSHA1(key);
    byte[] byteArray = Encoding.ASCII.GetBytes(input);
    MemoryStream stream = new MemoryStream(byteArray);
    return myhmacsha1.ComputeHash(stream).Aggregate("", (s, e) => s + String.Format("{0:x2}", e), s => s);
}