support ForwardedHeaders configuration

src/DefaultBuilder/src/ForwardedHeadersOptionsSetup.cs

@@ -24,7 +24,24 @@ public void Configure(ForwardedHeadersOptions options)
             return;
         }
 
-        options.ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto;
+        var forwardedHeaders = _configuration["ForwardedHeaders_Headers"];
+        if (string.IsNullOrEmpty(forwardedHeaders))
+        {
+            options.ForwardedHeaders = ForwardedHeaders.XForwardedFor | ForwardedHeaders.XForwardedProto;
+        }
+        else
+        {
+            var headers = ForwardedHeaders.None;
+            foreach (var headerName in forwardedHeaders.Split(',', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries))
+            {
+                if (Enum.TryParse<ForwardedHeaders>(headerName, true, out var headerValue))
+                {
+                    headers |= headerValue;
+                }
+            }
+            options.ForwardedHeaders = headers;
+        }
+
         // Only loopback proxies are allowed by default. Clear that restriction because forwarders are
         // being enabled by explicit configuration.
         options.KnownNetworks.Clear();

src/DefaultBuilder/test/Microsoft.AspNetCore.Tests/WebHostTests.cs

@@ -83,6 +83,38 @@ public async Task WebHostConfiguration_EnablesForwardedHeadersFromConfig()
         result.EnsureSuccessStatusCode();
     }
 
+    [Fact]
+    public async Task WebHostConfiguration_EnablesForwardedHeaders_CustomHeaders_FromConfig()
+    {
+        using var host = WebHost.CreateDefaultBuilder()
+            .ConfigureAppConfiguration(configBuilder =>
+            {
+                configBuilder.AddInMemoryCollection(new[]
+                {
+                    new KeyValuePair<string, string>("FORWARDEDHEADERS_ENABLED", "true" ),
+                    new KeyValuePair<string, string>("FORWARDEDHEADERS_HEADERS", "All" ),
+                });
+            })
+            .UseTestServer()
+            .Configure(app =>
+            {
+                Assert.True(app.Properties.ContainsKey("ForwardedHeadersAdded"), "Forwarded Headers");
+                app.Run(context =>
+                {
+                    Assert.Equal("https", context.Request.Scheme);
+                    Assert.Equal("/test", context.Request.PathBase.Value);
+                    return Task.CompletedTask;
+                });
+            }).Build();
+
+        await host.StartAsync();
+        var client = host.GetTestClient();
+        client.DefaultRequestHeaders.Add("x-forwarded-proto", "https");
+        client.DefaultRequestHeaders.Add("x-forwarded-prefix", "/test");
+        var result = await client.GetAsync("http://localhost/");
+        result.EnsureSuccessStatusCode();
+    }
+
     [Fact]
     public void CreateDefaultBuilder_RegistersRouting()
     {