_LoginPartial.cshtml

@using Microsoft.AspNet.Identity
@using PS_Esports.Utils
@using System.Security.Claims
@using System.Security.Principal


@if (Request.IsAuthenticated)
{
    using (Html.BeginForm("LogOff", "Account", FormMethod.Post, new { id = "logoutForm", @class = "navbar-right" }))
    {
    @Html.AntiForgeryToken()

    <ul class="nav navbar-nav navbar-right">
        <li>
            @Html.ActionLink("Hello " + @User.Identity.GetTag() + "!", "Index", "Manage", routeValues: null, htmlAttributes: new { title = "Manage" })
        </li>
        <li><a href="javascript:document.getElementById('logoutForm').submit()">Log off</a></li>
    </ul>
    }
}
else
{
    <ul class="nav navbar-nav navbar-right">
        <li>@Html.ActionLink("Register", "Register", "Account", routeValues: null, htmlAttributes: new { id = "registerLink" })</li>
        <li>@Html.ActionLink("Log in", "Login", "Account", routeValues: null, htmlAttributes: new { id = "loginLink" })</li>
    </ul>
}

AccountController.cs

        [HttpPost]
        [AllowAnonymous]
        [ValidateAntiForgeryToken]
        public async Task<ActionResult> Register(RegisterViewModel model)
        {
            if (ModelState.IsValid)
            {
                var user = new ApplicationUser { UserName = model.Email, Email = model.Email, Tag = model.tag};
                var person = new Person(model.tag);
                _context.Persons.Add(person);
                _context.SaveChanges();
                var result = await UserManager.CreateAsync(user, model.Password);
                if (result.Succeeded)
                {
                    await SignInManager.SignInAsync(user, isPersistent:false, rememberBrowser:false);
                    
                    // For more information on how to enable account confirmation and password reset please visit http://go.microsoft.com/fwlink/?LinkID=320771
                    // Send an email with this link
                    // string code = await UserManager.GenerateEmailConfirmationTokenAsync(user.Id);
                    // var callbackUrl = Url.Action("ConfirmEmail", "Account", new { userId = user.Id, code = code }, protocol: Request.Url.Scheme);
                    // await UserManager.SendEmailAsync(user.Id, "Confirm your account", "Please confirm your account by clicking <a href=\"" + callbackUrl + "\">here</a>");
                    UserManager.AddClaim(user.Id, new Claim("Tag", user.tag));
                    return RedirectToAction("Index", "Home");
                }
                AddErrors(result);
            }

            // If we got this far, something failed, redisplay form
            return View(model);
        }

ClaimsPrincipleExtension.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Claims;
using System.Security.Principal;
using System.Web;
using Microsoft.AspNet.Identity;

namespace PS_Esports.Utils
{
    public static class ClaimsPrincipleExtension
    {
        public static string GetTag(this IIdentity identity) {
            var claim = ((ClaimsIdentity) identity).Claims.Where(o => o.Type == "Tag").FirstOrDefault();
            return (claim != null) ? claim.Value : string.Empty;
        }
    }
}