ASP.NET: How to create form authentication cookie and set HttpContext.User

AuthenticationController.cs

[HttpGet]
public IHttpActionResult Authentication(string userName, string password)
{
    // Authenticate by any application specific logic, like calling to a a database and validating username and password
    var appUser = DbAuthentication(userName, password);
    SetAuthenticationCookie(appUser);
}

private static void SetAuthenticationCookie(Security.AppUser user)
{
    JObject data = new JObject();
    data["UserId"] = user.UserId;
    data["FullName"] = user.FullName;
    data["TokenId"] = user.TokenId;
    data["Roles"] = new JArray(user.Roles);
    var userData = data.ToString(Formatting.None);
    FormsAuthenticationTicket tkt = new FormsAuthenticationTicket(1, user.UserName, DateTime.Now, DateTime.Now.AddMinutes(120), true, userData);
    string cookiestr = FormsAuthentication.Encrypt(tkt);
    HttpCookie ck = new HttpCookie(FormsAuthentication.FormsCookieName, cookiestr);
    ck.Expires = tkt.Expiration;
    ck.Path = FormsAuthentication.FormsCookiePath;
    HttpContext.Current.Response.Cookies.Add(ck);
}

Global.asax.cs

protected void Application_AuthenticateRequest(object sender, EventArgs e)
{
    HttpCookie authCookie = Context.Request.Cookies[FormsAuthentication.FormsCookieName];
    string userId = null;
    string fullName = null;
    string tokenId = null;
    string[] roles = null;
    if (authCookie != null)
    {
        var authTicket = FormsAuthentication.Decrypt(authCookie.Value);
        if (authTicket.Version == 1)
        {
            JObject data = JObject.Parse(authTicket.UserData);
            userId = (string)data["UserId"];
            fullName = (string)data["FullName"];
            tokenId = (string)data["TokenId"];
            roles= data["Roles"].ToObject<string[]>();
        }
        
        // Security.AppUser class must implement System.Security.Principal
        Security.AppUser userPrincipal = new Security.AppUser(
            new GenericIdentity(authTicket.Name),
            fullName,
            new Guid(userId),
            new Guid(tokenId),
            roles);
        Context.User = userPrincipal;
       
        //Now you can access current authenticated user by the User property in the controllers. HttpContext.User 
        
    }
}