Startup.cs

namespace GraphQL.AspNet.Examples.CustomHttpProcessor
{
    using GraphQL.AspNet.Configuration;
    using Microsoft.AspNetCore.Builder;
    using Microsoft.AspNetCore.Hosting;
    using Microsoft.Extensions.Configuration;
    using Microsoft.Extensions.DependencyInjection;
    using Microsoft.Extensions.Hosting;

    public class Startup
    {
        private const string ALL_ORIGINS_POLICY = "_allOrigins";

        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            // apply an unrestricted cors policy for the demo services
            // to allow use on many of the tools for testing (graphiql, altair etc.)
            // Do not do this in production
            services.AddCors(options =>
            {
                options.AddPolicy(
                    ALL_ORIGINS_POLICY,
                    builder =>
                    {
                        builder.AllowAnyOrigin()
                        .AllowAnyHeader()
                        .AllowAnyMethod();
                    });
            });

            services.AddControllers();

            // Register the custom processor at startup
            services.AddGraphQL(options =>
            {
                options.QueryHandler.HttpProcessorType = typeof(CustomHttpProcessor);
            });
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.UseHttpsRedirection();

            app.UseRouting();

            app.UseCors(ALL_ORIGINS_POLICY);

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });

            app.UseGraphQL();
        }
    }
}