How to create your own App Service Site Extension in Azure?

Question

Please forward me some links/how-to guides for developing your own App service site extension for Azure. I am trying to intercept HTTP traffic going to/coming out from my App service and do some pre-checks / alter a few things as a part of the extension.

I didn't find any documents on developing your custom extension for Microsoft Azure App Service.

Can this extension be implemented in Golang? If yes, please share examples too.

Answer 1

In order to add the custom extension that intercepts the Http Requests in your application, You need to create one custom Nuget package built with your extension and publish it as a package in nuget.org.

I created one Asp.NET MVC application:-

Added one class that intercepts traffic:-

TrafficInterceptorMiddleware.cs:-

using Microsoft.AspNetCore.Http;
using System.Threading.Tasks;

public class TrafficInterceptorMiddleware
{
    private readonly RequestDelegate _next;

    public TrafficInterceptorMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        // Perform pre-checks or modifications here before the request is processed

        if (context.Request.Path.StartsWithSegments("/admin"))
        {
            // Perform pre-checks for requests to /admin endpoint
            // For instance, you can perform authentication, logging, etc.
            // Example: 
            // Check if the user is authenticated
            if (!context.User.Identity.IsAuthenticated)
            {
                context.Response.StatusCode = StatusCodes.Status401Unauthorized;
                await context.Response.WriteAsync("Unauthorized Access");
                return;
            }
        }

        // Before handling the request further, you can put your logic here.

        await _next(context);

        // Perform actions after the response has been generated (if needed)
        // For example:
        // Log response details, modify response headers, etc.
    }
}

Called this package in my Program.cs:-

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

var builder = WebApplication.CreateBuilder(args);

// Add services
builder.Services.AddControllersWithViews();

var app = builder.Build();

// Add middleware to the pipeline
app.UseMiddleware<TrafficInterceptorMiddleware>();

// Configure routes and endpoints
app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

app.Run();

Now, I built this project and added the .dll path in the .nuspec file.

Create one .nuspec file with the contents below:-

Traffic.nuspec

In order for your package to be added in Azure Site Extension add this line of code in your .nuspec:-

<tags>AzureSiteExtension</tags>
        <packageTypes>
            <packageType name="AzureSiteExtension" />
        </packageTypes>

Complete code:-

<?xml version="1.0"?>
<package>
    <metadata>
        <id>YourMiddlewarePackageId</id>
        <version>1.0.0</version>
        <title>TrafficInterceptorMiddleware</title>
        <authors>Siddhesh</authors>
        <owners>Siddhesh</owners>
        <requireLicenseAcceptance>false</requireLicenseAcceptance>
        <description>Middleware for intercepting HTTP traffic in ASP.NET 6.0 applications.</description>
        <dependencies>
            <dependency id="Microsoft.AspNetCore.Http" version="6.0.0" />
        </dependencies>
        <releaseNotes>Release notes for version 1.0.0.</releaseNotes>
        <tags>AzureSiteExtension</tags>
        <packageTypes>
            <packageType name="AzureSiteExtension" />
        </packageTypes>
    </metadata>
    <files>
        <file src="bin\Debug\net6.0\WebApplication40.dll" target="lib\net6.0" />
        <file src="README.md" target="" />
    </files>
</package>

Now, Add run the command below in your nuget CLI:-

You can add nuget.exe in your current project and run the command from the Visual Studio Command Line tool too:-

nuget pack Traffic.nuspec

Output:-

I directly uploaded the package by logging into my Nuget account by referring this MS Document:-

After uploading your package will get validated > published > indexed > publicly available:-

After your package is published, Visit your Azure extensions page and the Package is visible for installation:-

In Advanced Tools Kudu > Site Extensions>

Reference:-

Site Extensions are moving to nuget.org by August 2018 · Issue #87 · Azure/app-service-announcements (github.com)