Fix: .NET 10 Preview 7 Authentication Failure In Umbraco

by Luna Greco 57 views

Hey everyone, let's dive into a critical issue affecting Umbraco CMS users on .NET 10 Preview 7. We're seeing a pesky 401 error that's preventing the login page from loading, effectively locking users out of their Umbraco installations. This isn't just a minor inconvenience; it's a high-priority problem that needs our immediate attention. So, let’s break down what’s happening, why it’s happening, and what we can do about it.

Understanding the Bug: The 401 Error Explained

When running Umbraco CMS with .NET 10 Preview 7 (specifically version 10.0.100-preview.7.25380.108), the application is failing to load the login page, returning a 401 status error instead of the expected redirect to the login page. This issue seems to stem from breaking changes in ASP.NET Core's authentication behavior, particularly how it handles applications with both UI and web API endpoints. The core problem lies in determining when to redirect to the login page versus when to return a 401 response. To understand the scope of the issue, we need to delve into the specifics of the environment and the affected versions.

The problem is rooted in how ASP.NET Core is handling authentication redirects versus 401 responses. In previous versions, the system might have been more lenient in redirecting to the login page, even when a 401 might have been more appropriate from an API perspective. However, with the changes in .NET 10 Preview 7, the behavior has become stricter, leading to the 401 error when a redirect was expected. This is a significant change because it directly impacts user accessibility and the overall functionality of Umbraco CMS. Imagine trying to access your site and being met with a blank page and a 401 error – not a great experience, right? The goal here is to ensure a smooth and secure login process, which requires us to understand and address these breaking changes head-on. The shift in authentication behavior requires us to re-evaluate our approach to handling user access and security within Umbraco. It’s not just about fixing a bug; it’s about ensuring that the system behaves predictably and securely under the new .NET Core paradigm. This means we need to dive deep into the configuration and middleware to ensure everything aligns with the new expectations of .NET 10.

Environment and Affected Versions: Pinpointing the Problem

  • .NET Version: 10.0.100-preview.7.25380.108
  • OS: Windows 11 24H2 (x64)
  • Issue Status: Confirmed reproducible

Let's talk about the environment where this bug is rearing its head. We're specifically looking at .NET version 10.0.100-preview.7.25380.108, running on Windows 11 24H2 (x64). The bad news is that the issue is confirmed reproducible, meaning it’s not just a one-off glitch. To really nail down the scope, we've put different versions through their paces:

Affected Versions Testing:

  • âś… Working versions:
    • Windows 10 21H2 AMD64 + dotnet-sdk-9.0.303: Pass
    • Windows 10 21H2 AMD64 + dotnet-sdk-10.0.100-preview.7.25374.104: Pass
  • ❌ Failing version:
    • Windows 10 21H2 AMD64 + dotnet-sdk-10.0.100-preview.7.25380.108: Fail

As you can see, we've got a clear culprit here: dotnet-sdk-10.0.100-preview.7.25380.108. Versions before this seem to be playing nice, but this specific preview is causing the 401 error. This pinpointing is crucial because it tells us exactly where to focus our efforts. We're not chasing a ghost; we've identified the source of the issue. This also helps us communicate the problem effectively to the community and the .NET team, providing them with the precise information they need to understand and address the bug. It’s like being a detective and finding the smoking gun – we know who the suspect is, and now we can build our case. The fact that older versions are working smoothly gives us a valuable point of comparison. We can analyze the differences between the working and failing versions to understand exactly what changed in dotnet-sdk-10.0.100-preview.7.25380.108 that triggered this authentication issue. This comparative analysis is a powerful tool in debugging and allows us to isolate the specific code changes that are responsible.

Expected vs. Actual Behavior: What Should Happen and What Does

So, what's the ideal scenario? The expected behavior is straightforward: when a user clicks the