Multitenant Azure AD issuer validation in ASP.NET Core

If you use Azure AD authentication and want to allow users from any tenant to connect to your ASP.NET Core application, you need to configure the Azure AD app as multi-tenant, and use a “wildcard” tenant id such as organizations or common in the authority URL: openIdConnectOptions.Authority = "https://login.microsoftonline.com/organizations/v2.0"; The problem when you do that is that with the default configuration, the token validation will fail because the issuer in the token won’t match the issuer specified in the OpenID metadata.

Making a WPF app using a SDK-style project with MSBuildSdkExtras

Ever since the first stable release of the .NET Core SDK, we’ve enjoyed a better C# project format, often called “SDK-style” because you specify a SDK to use in the project file. It’s still a .csproj XML file, it’s still based on MSBuild, but it’s much more lightweight and much easier to edit by hand. Personally, I love it and use it everywhere I can. However, out of the box, it’s only usable for some project types: ASP.

Asynchronous initialization in ASP.NET Core, revisited

Initialization in ASP.NET Core is a bit awkward. There are well defined places for registering services (the Startup.ConfigureServices method) and for building the middleware pipeline (the Startup.Configure method), but not for performing other initialization steps (e.g. pre-loading data, seeding a database, etc.). Using a middleware: not such a good idea Two months ago I published a blog post about asynchronous initialization of an ASP.NET Core app using a custom middleware. At the time I was rather pleased with my solution, but a comment from Frantisek made me realize it wasn’t such a good approach.

Handling multipart requests with JSON and file uploads in ASP.NET Core

Suppose we’re writing an API for a blog. Our “create post” endpoint should receive the title, body, tags and an image to display at the top of the post. This raises a question: how do we send the image? There are at least 3 options: Embed the image bytes as base64 in the JSON payload, e.g. { "title": "My first blog post", "body": "This is going to be the best blog EVER!

Asynchronous initialization in ASP.NET Core with custom middleware

Update: I no longer recommend the approach described in this post. I propose a better solution here: Asynchronous initialization in ASP.NET Core, revisited. Sometimes you need to perform some initialization steps when your web application starts. However, putting such code in the Startup.Configure method is generally not a good idea, because: There’s no current scope in the Configure method, so you can’t use services registered with “scoped” lifetime (this would throw an InvalidOperationException: Cannot resolve scoped service ‘MyApp.

Hosting an ASP.NET Core 2 application on a Raspberry Pi

As you probably know, .NET Core runs on many platforms: Windows, macOS, and many UNIX/Linux variants, whether on x86/x64 architectures or on ARM. This enables a wide range of interesting scenarios… For instance, is a very small machine like a Raspberry Pi, which its low performance ARM processor and small amount of RAM (1 GB on my RPi 2 Model B), enough to host an ASP.NET Core web app? Yes it is!

Writing a GitHub Webhook as an Azure Function

I recently experimented with Azure Functions and GitHub apps, and I wanted to share what I learned. A bit of background As you may already know, I’m one of the maintainers of the FakeItEasy mocking library. As is common in open-source projects, we use a workflow based on feature branches and pull requests. When a change is requested in a PR during code review, we usually make the change as a fixup commit, because it makes it easier to review, and because we like to keep a clean history.

Understanding the ASP.NET Core middleware pipeline

Middlewhat? The ASP.NET Core architecture features a system of middleware, which are pieces of code that handle requests and responses. Middleware are chained to each other to form a pipeline. Incoming requests are passed through the pipeline, where each middleware has a chance to do something with them before passing them to the next middleware. Outgoing responses are also passed through the pipeline, in reverse order. If this sounds very abstract, the following schema from the official ASP.

Cleanup Git history to remove unwanted files

I recently had to work with a Git repository whose modifications needed to be ported to another repo. Unfortunately, the repo had been created without a .gitignore file, so a lot of useless files (bin/obj/packages directories…) had been commited. This made the history hard to follow, because each commit had hundreds of modified files. Fortunately, it’s rather easy with Git to cleanup a branch, by recreating the same commits without the files that shouldn’t have been there in the first place.

Better timeout handling with HttpClient

The problem If you often use HttpClient to call REST APIs or to transfer files, you may have been annoyed by the way this class handles request timeout. There are two major issues with timeout handling in HttpClient: The timeout is defined at the HttpClient level and applies to all requests made with this HttpClient; it would be more convenient to be able to specify a timeout individually for each request.