How to authorize SignalR Core Hub method with JWT

Question

I am using JWT authentication in my ASP.NET Core 2.0 application with OpenIddict.

I am following idea in this thread and calling AuthorizeWithJWT method after SignalR handshake. But now, I do not know what should I set in AuthorizeWithJWT method so I can use [Authorize(Roles="Admin")] for example.

I tried with setting context user, but it is readonly:

public class BaseHub : Hub
{    
    public async Task AuthorizeWithJWT(string AccessToken)
    {
        //get user claims from AccesToken
        this.Context.User = user;  //error User is read only
    }
}

And using authorize attribute:

public class VarDesignImportHub : BaseHub
{
    [Authorize(Roles = "Admin")]
    public async Task Import(string ConnectionString)
    {
    }
}

Answer 1

I strongly encourage you to continue doing authentication at the handshake level instead of going with a custom and non-standard solution you'd implement at the SignalR level.

Assuming you're using the validation handler, you can force it to retrieve the access token from the query string:

public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication()
        .AddOAuthValidation(options =>
        {
            options.Events.OnRetrieveToken = context =>
            {
                context.Token = context.Request.Query["access_token"];

                return Task.CompletedTask;
            };
        });
}

Or OnMessageReceived if you want to use JWTBearer:

services.AddAuthentication()
    .AddJwtBearer(o =>
    {
        o.Events = new JwtBearerEvents()
        {
            OnMessageReceived = context =>
            {
                if (context.Request.Path.ToString().StartsWith("/HUB/"))
                    context.Token = context.Request.Query["access_token"];
                return Task.CompletedTask;
            },
        };
    });

No other change should be required.