How to authorize SignalR Core Hub method with JWT - authentication

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.