public class SignalrQsHeaderMiddleware
{
    private readonly RequestDelegate _next;

    public SignalrQsHeaderMiddleware(RequestDelegate next)
    {
        this._next = next;
    }

    public async Task Invoke(HttpContext context)
    {
        /*
        if (context.Request.Path.Value.Contains("/restaurantHub"))
        {
            var qsHeader = context.Request.Query["access_token"].ToString();
            if (!qsHeader.IsNullOrEmpty())
            {
                context.Request.Headers.Add("Authorization",qsHeader);
            }
        }*/
        await _next.Invoke(context);

    }
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    //Other services.
    app.UseMiddleware<SignalrQsHeaderMiddleware>();//<-- added here
}