How to fix Can't find Request.GetOwinContext in Web API

You need to ensure that you're using the right namespaces to access GetOwinContext(). Make sure you have the following namespaces included in your code file:

using Microsoft.AspNet.Identity.Owin;
using Microsoft.AspNet.Identity;

You should install Microsoft.AspNet.Identity.Owin from the Nuget Package Manager into your project.

If you're getting an error when trying to retrieve the UserManager from the OwinContext in an ApiController in ASP.NET MVC, there are several potential causes and solutions. The issue usually arises because the OWIN context might not be correctly configured, or you're trying to access UserManager incorrectly.

If you're using dependency injection properly, you should get ApplicationUserManager and ApplicationSignInManager via constructor injection.

using System.Web;
using System.Web.Http;
using Microsoft.AspNet.Identity.Owin;
using System.Linq;
using System;
using System.Threading.Tasks;
using Microsoft.AspNet.Identity;

namespace Invoice.Controllers
{
    public class AccountController : ApiController
    {
        private ApplicationSignInManager _signInManager;
        private ApplicationUserManager _userManager;

        // Constructor injection for UserManager and SignInManager
        public AccountController(ApplicationUserManager userManager, ApplicationSignInManager signInManager)
        {
            UserManager = userManager;
            SignInManager = signInManager;
        }

        public ApplicationSignInManager SignInManager
        {
            get
            {
                // If _signInManager is not set, get it from OwinContext
                return _signInManager ?? HttpContext.Current.GetOwinContext().Get<ApplicationSignInManager>();
            }
            private set
            {
                _signInManager = value;
            }
        }
        
        public ApplicationUserManager UserManager
        {
            get
            {
                // getowincontext httpcontext.current.getowincontext()
                return _userManager ?? HttpContext.Current.GetOwinContext().GetUserManager<ApplicationUserManager>();
            }
            private set
            {
                _userManager = value;
            }
        }        
    }
}

Remember replace HttpContext.GetOwinContext().Get<ApplicationSignInManager>() to HttpContext.Current.GetOwinContext().Get<ApplicationSignInManager>()