Object as a Scoped Service, With Values being Set in Middleware, Sometimes Remains Null

I use the following to create an instance of a class for storing user information during the request:

services.AddScoped<IUserSettings, UserSettings>();

Then I use middleware to set the values of the userSettings.

public async Task InvokeAsync(HttpContext context, IUserSettings userSettings, IHttpClientFactory httpClientFactory)
{
    // Do some stuff here and set userSettings properties
}

The problem is when I send multiple requests in parallel, only one of them gets a non null userSettings.

Why does this happen and how can I fix it?

As of now I use httpContext.Items to store and use userSettings.

According to the document:

To use scoped services in middleware, use one of the following approaches:

• Inject the service into the middleware's Invoke or InvokeAsync method. Using constructor injection throws a runtime exception because it forces the scoped service to behave like a singleton. The sample in the Lifetime and registration options section demonstrates the InvokeAsync approach.
• Use Factory-based middleware. Middleware registered using this approach is activated per client request (connection), which allows scoped services to be injected into the middleware's constructor.

So I suggest you could modify your middleware to use Factory-based middleware to see if we could solve this issue.

More details, you could refer to below example:

Usersettings:

public interface IUserSettings
{
    string UserId { get; set; }
    string UserName { get; set; }
  
}

// UserSettings.cs
public class UserSettings : IUserSettings
{
    public string UserId { get; set; }
    public string UserName { get; set; }
}

Usersettings middleware:

public class UserSettingsMiddleware : IMiddleware
{
    private readonly IUserSettings _userSettings;

    public UserSettingsMiddleware(IUserSettings userSettings)
    {
        _userSettings = userSettings;
    }

    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
    {
        _userSettings.UserId = "123";
        _userSettings.UserName = "John Doe";

    
        await next(context);
    }
}

MiddlewareExtensions:

public static class MiddlewareExtensions
{
  

    public static IApplicationBuilder UseUserSettingsMiddleware(
        this IApplicationBuilder app)
        => app.UseMiddleware<UserSettingsMiddleware>();
}

Register inside the program.cs:

...
builder.Services.AddScoped<IUserSettings, UserSettings>();
builder.Services.AddTransient<UserSettingsMiddleware>();
...

app.UseUserSettingsMiddleware();

Result: