Adds option to CocoonProxyOptions to control the request Host header …

…value. Fixes VisualReCode#30

main/src/ReCode.Cocoon.Proxy/Proxy/CocoonProxy.cs

@@ -1,12 +1,12 @@
-using System;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc.ModelBinding.Binders;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging;
+using System;
 using System.Collections.Generic;
-using System.Diagnostics;
 using System.Net;
 using System.Net.Http;
 using System.Threading.Tasks;
-using Microsoft.AspNetCore.Http;
-using Microsoft.Extensions.Configuration;
-using Microsoft.Extensions.Logging;
 using Yarp.ReverseProxy.Forwarder;
 
 namespace ReCode.Cocoon.Proxy.Proxy
@@ -19,6 +19,8 @@ public class CocoonProxy
         private readonly RedirectTransformer _transformer;
         private readonly ForwarderRequestConfig _requestConfig;
         private readonly string _destinationPrefix;
+        private readonly HostHeaderOptions _hostHeaderOption;
+        private readonly string _host;
 
         public CocoonProxy(IConfiguration configuration, ILogger<CocoonProxy> logger, IHttpForwarder httpForwarder, CocoonProxyOptions? proxyOptions)
         {
@@ -36,7 +38,11 @@ public CocoonProxy(IConfiguration configuration, ILogger<CocoonProxy> logger, IH
                 throw new InvalidOperationException("Invalid DestinationPrefix");
             }
 
-            logger.LogInformation($"Cocoon Proxy backend: {destinationPrefixUri}");
+            logger.LogInformation("Cocoon Proxy backend: {destinationPrefixUri}", destinationPrefixUri);
+
+            // save the host
+            _host = destinationPrefixUri.Host;
+            logger.LogInformation("Cocoon Proxy backend: host is {host}", _host);
 
             _backendUrls = CocoonProxyExclusions.CreateExclusionSet(configuration);
 
@@ -57,6 +63,9 @@ public CocoonProxy(IConfiguration configuration, ILogger<CocoonProxy> logger, IH
             _httpClient = new HttpMessageInvoker(socketsHttpHandler);
             _transformer = new RedirectTransformer(destinationPrefixUri);
 
+            // save the host header option, or use default option
+            _hostHeaderOption = proxyOptions?.HostHeaderOption ?? HostHeaderOptions.None;
+
             if (!TimeSpan.TryParse(configuration.GetValue<string>("Cocoon:Proxy:Timeout"), out var timeout))
             {
                 timeout = TimeSpan.FromSeconds(30);
@@ -75,10 +84,42 @@ public async Task ProxyAsync(HttpContext httpContext)
                 return;
             }
 
+            // amend the HOST value in the request based on _hostHeaderOption
+            switch (_hostHeaderOption)
+            {
+                case HostHeaderOptions.None:
+                    // HostHeader unchanged
+                    break;
+
+                case HostHeaderOptions.SetDefault:
+                    // HostHeader set to default
+                    SetHost(httpContext.Request.Headers, default);
+                    break;
+
+                case HostHeaderOptions.UseHost:
+                    // HostHeader set to _host
+                    SetHost(httpContext.Request.Headers, _host);
+                    break;
+
+                default:
+                    // unhandled options not supported
+                    throw new NotSupportedException($"Unhandled HostHeaderOption {_hostHeaderOption}");
+            }
+
             using var activity = ProxyActivitySource.StartActivity("Proxy");
             activity?.SetTag("path", httpContext.Request.Path.ToString());
 
             await _httpForwarder.SendAsync(httpContext, _destinationPrefix, _httpClient, _requestConfig, _transformer);
         }
+
+        /// <summary>
+        /// NET6 has useful 
+        /// </summary>
+        /// <param name="headers"></param>
+        /// <param name="host"></param>
+        private static void SetHost(IHeaderDictionary headers, string? host)
+        {
+            headers["Host"] = host;
+        }
     }
 }

main/src/ReCode.Cocoon.Proxy/Proxy/CocoonProxyOptions.cs

@@ -5,5 +5,10 @@ namespace ReCode.Cocoon.Proxy.Proxy
     public class CocoonProxyOptions
     {
         public RemoteCertificateValidationCallback? RemoteCertificateValidationCallback { get; set; }
+
+        /// <summary>
+        /// Set Host header behaviour
+        /// </summary>
+        public HostHeaderOptions HostHeaderOption { get; set; } = HostHeaderOptions.None;
     }
 }

main/src/ReCode.Cocoon.Proxy/Proxy/HostHeaderOptions.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace ReCode.Cocoon.Proxy.Proxy
+{
+    /// <summary>
+    /// Host Header options when proxying request
+    /// </summary>
+    /// <remarks>
+    /// Fixes #30 https://github.com/VisualReCode/Cocoon/issues/30
+    /// </remarks>
+    public enum HostHeaderOptions
+    {
+        /// <summary>
+        /// Default operation: no changes to Host header
+        /// </summary>
+        None,
+        /// <summary>
+        /// Used on Azure hosting: sets the Host header to `default` (null)
+        /// </summary>
+        SetDefault,
+        /// <summary>
+        /// Copies the host header from the request to the Cocoon proxy
+        /// </summary>
+        UseHost
+    }
+}