How to Properly Inject UserManager Into Program.cs or Startup.cs in ASP.NET Core

Learn the best practices for injecting `UserManager` in ASP.NET Core applications without creating unnecessary service instances. Find out how to streamline your application while maintaining efficiency!
---

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---

When building an ASP.NET Core application, you might encounter situations where you need to inject services such as UserManager into your application's configuration methods. This is particularly important for authentication purposes, where you may need to validate user details during authentication events. A common challenge developers face is how to do this effectively without causing issues like service duplication or performance bottlenecks.

The Problem

In your ConfigureServices method, you may have attempted to create a new service provider with BuildServiceProvider() to resolve UserManager<MyUser>. While this might work, it triggers a warning (ASP0000) indicating that building a provider from application code could lead to instantiating additional copies of singleton services, which is not a good practice.

Why Is This a Problem?

Multiple Instances: Creating a new service provider results in additional instances of services, potentially leading to memory leaks and inconsistent behavior in your application.

Performance Issues: Resolving services this way during a handler execution can degrade performance, as creating a provider is generally an expensive operation.

The Solution

Instead of building a new service provider, you can utilize the existing service provider that is available within the HTTP context. Here’s how you can do it.

Revised Code Example

Replace your existing code with this streamlined approach using the HttpContext.RequestServices property:

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

Breakdown of the Code

Accessing the Existing UserManager Instance:
Use context.HttpContext.RequestServices.GetRequiredService<UserManager<MyUser>>() to retrieve the UserManager directly from the established service provider linked to the current HTTP request.

User Validation Logic:
After acquiring the UserManager, you can fetch the relevant user details and execute your validation logic, such as checking if the user has confirmed their email.

Conclusion

By injecting the UserManager directly from the services contained in the HTTP context, you not only adhere to best practices in service management but also enhance the overall performance and reliability of your application. Avoiding the creation of additional service providers simplifies your code and removes unnecessary risks.

With this approach, you can effectively manage user authentication scenarios and ensure your web application remains efficient and well-structured. Happy coding!