This is a .NET Core overhaul of my old PayPalHelper project. The Nuget package is AO.PayPalHelper.

The thing to use here is an HttpRequest extension method called VerifyPayPalTransactionAsync. This returns a VerificationResult.

[FunctionName("IpnHandler")]
public static async Task<IActionResult> Run(
    [HttpTrigger(AuthorizationLevel.Anonymous, "post")] HttpRequest req,
    ILogger log)
{
    var result = await req.VerifyPayPalTransactionAsync(PayPalEnvironment.Sandbox, log);
    if (result.IsVerified)
    {
        log.LogInformation("yes it's verified!");
        log.LogInformation($"the buyer is {result.Transaction.PayerEmail}, and they paid {result.Transaction.Gross} for item {result.Transaction.ItemNumber}");
    }
    else
    {
        log.LogInformation("no, not verified");
    }
    return new OkResult();
}

You can see an example in my little Azure Function test project.

There is also an IpnController abstract class you can implement. This is sort of compatible with the approach in my old project, but nowadays I lean toward Azure Functions, and I like how lightweight a single extension method is.

I don't have a unit test project, and I haven't tried this with real PayPal transactions yet. But I have tested with Ngrok and PayPal's own IPN simulator. Microsoft has a great walkthrough on using Ngrok to test Azure Functions locally, and that's what I worked from.

Note that I didn't try to implement every single IPN variable on my PayPalTransaction model class. I just addded the important ones I'm familiar with that jumped out at me from PayPal's reference.

Here's a video walkthrough that doubles as a crash course into to Azure Functions: Vimeo.

As of 3/12/20, I have a realistic use case in my CloudLicensing project.