How to pass value instead of access token in SignalR HubConnectionBuilder

Question

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();

Answer 1

Is it too late to answer this?

You can use any string as a token, so you can do:

let connection = new signalR.HubConnectionBuilder()
    .withUrl("/chathub", {
        accessTokenFactory: () => {
            return "this:is:my:token";
        }
    })
    .build();

and then on your server you can have

public class CustomTokenSchemeHandler : AuthenticationHandler<CustomTokenSchemeOptions>
{
...
    protected override async Task<AuthenticateResult> HandleAuthenticateAsync()
    {
        var messageReceivedContext = new MessageReceivedContext(Context, Scheme, Options);

        var token = Context.Request.Headers["Authorization"].ToString().Replace("Bearer ", "");

        if (token is null)
        {
            return AuthenticateResult.NoResult();
        }

        string[] userInfoArray = token.Split(":");

        var claims = new[]
        {
            new Claim(ClaimTypes.Name, userInfoArray[1]),
            new Claim(ClaimTypes.Sid, userInfoArray[0])
// add whatever else you want here
        };
        var principal = new ClaimsPrincipal(new ClaimsIdentity(claims, Scheme.Name));
        var ticket = new AuthenticationTicket(principal, Scheme.Name);
        return AuthenticateResult.Success(ticket);
    }
...
}

and in your services configuration:

builder.Services.AddAuthentication("CustomToken")
    .AddScheme<CustomTokenSchemeOptions, CustomTokenSchemeHandler>("CustomToken");

more or less. Some connecting elements/boilerplate code is probably missing but this should give you the general idea how to go about this.