As it is mention in the MS doc you can authorize your SignalR with access token like this:

let connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub", {
        accessTokenFactory: () => {
            // Get and return the access token.
            // This function can return a JavaScript Promise if asynchronous
            // logic is required to retrieve the access token.
        }
    })
    .build();

and you can use in your backend code (with IUserIdProvider) like this

public class EmailBasedUserIdProvider : IUserIdProvider
{
    public virtual string GetUserId(HubConnectionContext connection)
    {
        return connection.User?.FindFirst(ClaimTypes.Email)?.Value!;
    }
}

I don't have a proper token to pass to the accessTokenFactory, but I have UserId on my client and I want to use this userIs with GetUserId method, so I could distinguish who the chat belongs to by UserId instead of whole Token. Is it possible to pass another value (or just a one claim) to HubConnectionBuilder? Like for example:

let connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub", {
        accessTokenFactory: () => {
            // Pass your value or just a custom claim so it could be retrive on server side
        }
    })
    .build();