How is SignalR aware of userID while EF Core Identity has been deployed as login system?

Alex Dunlop

I'm using EF Core Identity as register/login system in my project. I tried to use signalR to push notification when a new message is send to a user. I have a form with two inputs, one for user who will receive the message and the other for the main message text. The message information is stored in the database and a notification is send to the client. I used the following codes: Adding signalR service to **program.cs**:

builder.Services.AddSignalR();
.
.
app.MapHub("/msgHub");

Code for **Hub**:

public class MessageHub : Hub
{
private readonly IUserRepository _userRepository;
private readonly ICostCenterRepository _costcenterRepository;

        public MessageHub(IUserRepository userRepository, ICostCenterRepository costcenterRepository)
        {
            \_userRepository = userRepository;
            \_costcenterRepository = costcenterRepository;
        }
        public async Task SendMessage(string costCenter)
        {
            string userId = \_userRepository.GetUserIdByCostCenter(costCenter).ToString();
            await Clients.User(userId).SendAsync("ReceiveMessage");
        }
    }

Code for **message.js**:

var connection = new signalR.HubConnectionBuilder().withUrl("/msgHub").withAutomaticReconnect().build();
connection.start();
document.getElementById("sendBtn").addEventListener("click", function () {
var costCenter = $("#cost-center").val();
connection.invoke("SendMessage", costCenter).catch(function (err) {
return console.error(err.tostring());
});
});

Script in the view:

    connection.on("ReceiveMessage", function () {
    location.reload();
    });
    connection.start().catch(function (err) {
    return console.error(err.tostring());
    });

Controller for sending message:

public JsonResult Send(string inputMessageText, string costCenter)
{
int CurrentUserId = Convert.ToInt32(HttpContext.Session.GetString("userId"));
int receiverId = _userRepository.GetUserIdByCostCenter(costCenter);

        if (!ModelState.IsValid)
        {
            return Json(new { success = false});
        }
        else
        {
            var newMessage = new Message()