support for X-Forwarded-Host header

allow to override the HTTP scheme and allow to override the url when the wsdl query is called

README.md

@@ -80,6 +80,7 @@ To use it, add a setting like this to appsettings
 ```json
 "FileWSDL": {
   "UrlOverride": "",
+  "SchemeOverride": "",
   "VirtualPath": "",
   "WebServiceWSDLMapping": {
     "Service.asmx": {
@@ -93,6 +94,7 @@ To use it, add a setting like this to appsettings
 ```
 
 * UrlOverride - can be used to override the URL in the service description. This can be useful if you are behind a firewall.
+* SchemeOverride - can be used to override the HTTP Scheme in the service description. This can be useful if you are behind a firewall and the firewall sets the X-Forwarded-Host header, but the internal HTTP scheme is not the same as the external.
 * VirualPath - can be used if you like to add a path between the base URL and service. 
 * WebServiceWSDLMapping
   * UrlOverride - can be used to override the URL for a specific WSDL mapping. This can be useful if you want to host different services under different folder.

src/SoapCore/SoapEndpointMiddleware.cs

@@ -4,6 +4,7 @@
 using System.IO;
 using System.Linq;
 using System.Net;
+using System.Net.Http;
 using System.Net.Http.Headers;
 using System.Reflection;
 using System.Runtime.CompilerServices;
@@ -20,6 +21,7 @@
 using Microsoft.AspNetCore.WebUtilities;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
 using Microsoft.Extensions.Primitives;
 using SoapCore.DocumentationWriter;
 using SoapCore.Extensibility;
@@ -984,16 +986,7 @@ private MetaFromFile GetMeta(HttpContext httpContext)
 
 			meta.WSDLFolder = mapping.WSDLFolder;
 			meta.XsdFolder = mapping.SchemaFolder;
-
-			if (options.UrlOverride != string.Empty)
-			{
-				meta.ServerUrl = options.UrlOverride;
-			}
-			else
-			{
-				meta.ServerUrl = httpContext.Request.Scheme + "://" + httpContext.Request.Host + "/";
-			}
-
+			meta.ServerUrl = options.GetServerUrl(httpContext);
 			return meta;
 		}
 
@@ -1072,16 +1065,9 @@ private async Task ProcessMetaFromFile(HttpContext httpContext, bool showDocumen
 				meta.CurrentWebService = mapping.UrlOverride;
 			}
 
-			meta.XsdFolder = mapping.SchemaFolder;
 			meta.WSDLFolder = mapping.WSDLFolder;
-			if (options.UrlOverride != string.Empty)
-			{
-				meta.ServerUrl = options.UrlOverride;
-			}
-			else
-			{
-				meta.ServerUrl = httpContext.Request.Scheme + "://" + httpContext.Request.Host + "/";
-			}
+			meta.XsdFolder = mapping.SchemaFolder;
+			meta.ServerUrl = options.GetServerUrl(httpContext);
 
 			string wsdlfile = mapping.WsdlFile;
 

src/SoapCore/WSDLFileOptions.cs

@@ -1,3 +1,4 @@
+using Microsoft.AspNetCore.Http;
 using System;
 using System.Collections.Generic;
 
@@ -7,8 +8,27 @@ public class WsdlFileOptions
 	{
 		public virtual Dictionary<string, WebServiceWSDLMapping> WebServiceWSDLMapping { get; set; } = new Dictionary<string, WebServiceWSDLMapping>();
 		public string UrlOverride { get; set; }
+		public string SchemeOverride { get; set; }
 		public string VirtualPath { get; set; }
 		public string AppPath { get; set; }
+
+		public virtual string GetServerUrl(HttpContext httpContext)
+		{
+			if (!string.IsNullOrEmpty(UrlOverride))
+			{
+				return UrlOverride;
+			}
+
+			string scheme = string.IsNullOrEmpty(SchemeOverride) ? httpContext.Request.Scheme : SchemeOverride;
+			string host = httpContext.Request.Host.ToString();
+			var forwardedHost = httpContext.Request.Headers["X-Forwarded-Host"];
+			if (forwardedHost.Count != 0)
+			{
+				host = forwardedHost[0];
+			}
+
+			return scheme + "://" + host + "/";
+		}
 	}
 
 	public class WsdlFileOptionsCaseInsensitive : WsdlFileOptions