Console app to generate a gateway to a service using NSwag and a swagger document.

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using NSwag;
using NSwag.CodeGeneration.CSharp;

namespace GatewayGenerator
{
    class Program
    {
        protected static string GetArg(List<string> argsList, string argName)
        {
            int index = -1;
            var pos = argsList.Select((s, i) => new {i, s})
                .Where(a => a.s == $"--{argName}")
                .FirstOrDefault();
            if (pos != null)
            {
                index = pos.i + 1;
            }

            var val = index != -1 ? argsList[index] : null;

            if (val == null || val.StartsWith("--"))
            {
                Console.WriteLine($"Missing arg --{argName}");
            }

            return val;
        }

        async static Task Main(string[] args)
        {
            if (args.Length > 0)
            {
                var argsList = new List<string>(args);

                // --url
                var swaggerUrl = GetArg(argsList, "url");
                if (swaggerUrl == null)
                {
                    return;
                }

                // --class-name
                var className = GetArg(argsList, "class-name");
                if (className == null)
                {
                    return;
                }

                // --namespace
                var namespaceValue = GetArg(argsList, "namespace");
                if (namespaceValue == null)
                {
                    return;
                }

                // --configuration-class
                var configurationClass = GetArg(argsList, "configuration-class");
                if (configurationClass == null)
                {
                    return;
                }

                System.Net.WebClient wclient = new System.Net.WebClient();
                var document = await OpenApiDocument.FromJsonAsync(wclient.DownloadString(swaggerUrl));

                wclient.Dispose();

                var settings = new CSharpClientGeneratorSettings
                {
                    ConfigurationClass = configurationClass,
                    ClassName = className,
                    InjectHttpClient = false, 
                    CSharpGeneratorSettings = 
                    {
                        Namespace = namespaceValue
                    },
                    UseHttpClientCreationMethod = true
                };

                var generator = new CSharpClientGenerator(document, settings);	
                var code = generator.GenerateFile();
                Console.WriteLine(code);
            }
            else
            {
                Console.WriteLine("Usage: GatewayGenerator --url <url to swagger.json>"
                    +" --class-name <e.g. SomeOtherServiceGateway>"
                    +" --namespace <e.g. SomeService.Gateways>"
                    +" --configuration-class <class name of configuration>");
            }
        } // end Main
    }
}