ASP.NET Core Middleware Passing Parameters to Controllers

Question

I am using ASP.NET Core Web API, where I have Multiple independent web api projects. Before executing any of the controllers' actions, I have to check if the the logged in user is already impersonating other user (which i can get from DB) and can pass the impersonated user Id to the actions.

Since this is a piece of code that gonna be reused, I thought I can use a middleware so:

• I can get the initial user login from request header
• Get the impesonated User Id if any
• Inject that ID in the request pipeline to make it available to the api being called

public class GetImpersonatorMiddleware
{
    private readonly RequestDelegate _next;
    private IImpersonatorRepo _repo { get; set; }

    public GetImpersonatorMiddleware(RequestDelegate next, IImpersonatorRepo imperRepo)
    {
        _next = next;
        _repo = imperRepo;
    }
    public async Task Invoke(HttpContext context)
    {
        //get user id from identity Token
        var userId = 1;

        int impersonatedUserID = _repo.GetImpesonator(userId);

        //how to pass the impersonatedUserID so it can be picked up from controllers
        if (impersonatedUserID > 0 )
            context.Request.Headers.Add("impers_id", impersonatedUserID.ToString());

        await _next.Invoke(context);
    }
}

I found this Question, but that didn't address what I am looking for.

How can I pass a parameter and make it available in the request pipeline? Is it Ok to pass it in the header or there is more elegant way to do this?

Solution 1

You can use HttpContext.Items to pass arbitrary values inside the pipeline:

context.Items["some"] = "value";

Solution 2

A better solution would be to use a scoped service. Take a look at this: Per-request middleware dependencies

Your code should look like:

public class MyMiddleware
{
    private readonly RequestDelegate _next;

    public MyMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext httpContext, IImpersonatorRepo imperRepo)
    {
        imperRepo.MyProperty = 1000;
        await _next(httpContext);
    }
}

And then register your ImpersonatorRepo as:

services.AddScoped<IImpersonatorRepo, ImpersonatorRepo>()

Comments

[poke]

See also: Working with HttpContext.Items

[Muhammad Saqib]

I'm using Session. context.Session.SetInt32("user-id", 12345); Which is the best approach and why?

[Ricardo Peres]

Sessions may or not be enabled, and they require cookies.

[Sven]

This is not working when you try to use the service per-request outside the middleware. See docs.microsoft.com/en-us/aspnet/core/fundamentals/middleware‌​/…

[Sven]

This seems still to be the only valid solution to store values outside the middleware pipeline.