Скачать или смотреть How to Retry a Request After Login in Blazor WASM

Discover how to handle 401 responses in Blazor WebAssembly by retrying requests after a successful login using JavaScript interop.
---
This video is based on the question https://stackoverflow.com/q/73325732/ asked by the user 'Zach' ( https://stackoverflow.com/u/1339964/ ) and on the answer https://stackoverflow.com/a/73409028/ provided by the user 'Zach' ( https://stackoverflow.com/u/1339964/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How do I retry a request after login?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Handling Unauthorized Requests in Blazor: Retries After Login

When building applications with Blazor WebAssembly (WASM), developers often face challenges with authentication, especially when dealing with requests that may return an unauthorized (401) status code. In particular, the goal is to seamlessly manage login scenarios without requiring users to refresh the page or click additional buttons.

In this guide, we will explore how to effectively implement a mechanism for retrying these unauthorized requests after a successful login, drawing inspiration from an Angular implementation and adapting it for C# .

Problem Overview

In an Angular single-page application (SPA), handling 401 responses with an HttpInterceptor enables automatic login prompts and request retries after user authentication. This creates a smooth user experience, making the application feel responsive and fluid. However, when transitioning to Blazor/C# , we must adopt a different approach, as Blazor does not provide direct equivalents to Angular's Observables and interceptors.

The key challenge is creating a flow where the original request is held until the login is successfully completed, allowing it to be retried automatically.

Solution Outline

We can tackle this problem in Blazor by implementing a DelegatingHandler that utilizes JavaScript interop to open a login window, handles the response, and retries the initial request once the user is authenticated.

Step 1: Create a Delegating Handler

First, we need to create a custom DelegatingHandler that will be responsible for checking response status codes and managing the login workflow:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Implement JavaScript for Handling Messages

To effectively manage messages between Blazor and JavaScript, we need to set up an event listener in JavaScript that communicates log-in success back to our C# code.

Here's the JavaScript snipped to handle the messages:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Creating the Sign-In Page

In a typical SSO setup, you would redirect to a sign-in page handled by your authentication provider:

[[See Video to Reveal this Text or Code Snippet]]

Step 4: Completing the Sign-In Process

After the user successfully logs in, the completed authentication will redirect back to a page where you can send a message back to the opener window (the original Blazor app):

[[See Video to Reveal this Text or Code Snippet]]

Conclusion

With this setup, we can now allow users to seamlessly authenticate in a Blazor WASM application by automatically retrying 401 requests after a successful login. This approach enhances user experience by mitigating the need to refresh the page or manually re-attempt actions.

Implementing this DelegatingHandler along with JavaScript interop creates a fluid authentication experience reminiscent of traditional SPAs, proving Blazor's capability to handle complex workflows elegantly.

If you find this implementation helpful, or if you have your own improvements, please share them in the comments!