.net core middleware for claims in csharp

main.cs
using System.Security.Claims;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;

public class AddClaimsMiddleware
{
    private readonly RequestDelegate _next;
    private readonly string _claimType;
    private readonly string _claimValue;

    public AddClaimsMiddleware(RequestDelegate next, string claimType, string claimValue)
    {
        _next = next;
        _claimType = claimType;
        _claimValue = claimValue;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        var identity = context.User.Identity as ClaimsIdentity;
        identity?.AddClaim(new Claim(_claimType, _claimValue));
        await _next(context);
    }
}

public static class AddClaimsMiddlewareExtensions
{
    public static IApplicationBuilder UseAddClaims(this IApplicationBuilder builder, string claimType, string claimValue)
    {
        return builder.UseMiddleware<AddClaimsMiddleware>(claimType, claimValue);
    }
}
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main.cs
public void Configure(IApplicationBuilder app)
{
    app.UseAuthentication();

    app.UseAddClaims("custom_claim", "some_value");

    app.UseMvc();
}
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