Added support for more advanced proxy configuration

Signed-off-by: arzumify <jliwin98@danwin1210.de>

config.yaml.example

@@ -88,10 +88,16 @@ routes: [
           url: "http://localhost:8000",
           # stripPrefix defines whether to strip the prefix from the path before proxying.
           stripPrefix: true
-            # TODO: In a future update, passing X-Forwarded-For and X-Forwarded-Proto headers will be supported.
-            # TODO: In a future update, forbidding certain headers from being passed will be supported.
-            # TODO: In a future update, passing X-Powered-By and Server headers will be supported.
-            # TODO: In a future update, passing Host header will be supported.
+          headers: {
+            # forbid defines the headers to forbid from being sent to the proxied server.
+            forbid: ["Authorization"],
+            # preserve defines the headers to preserve when sending to the client.
+            preserve: [X-Powered-By", "Server"]
+            # host defines whether the host / :authority header should be sent to the proxied server.
+            host: true,
+            # xForward defines whether to send the X-Forwarded-For and X-Forwarded-Proto headers.
+            xForward: true
+          }
         },
         {
           # path defines the path to match. They can contain wildcards.

main.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	library "git.ailur.dev/ailur/fg-library/v2"
+	"net/http/httputil"
+	"net/url"
 
 	"errors"
 	"io"
@@ -18,8 +20,6 @@ import (
 	"database/sql"
 	"log/slog"
 	"net/http"
-	"net/http/httputil"
-	"net/url"
 	"path/filepath"
 
 	"github.com/go-chi/chi/v5"
@@ -79,6 +79,7 @@ type Config struct {
 			Proxy struct {
 				URL         string         `yaml:"url" validate:"required"`
 				StripPrefix bool           `yaml:"stripPrefix"`
+				Headers     HeaderSettings `yaml:"headers"`
 			} `yaml:"proxy" validate:"required_without=Static Redirect"`
 			Static struct {
 				Root             string `yaml:"root" validate:"required,isDirectory"`
@@ -101,6 +102,15 @@ type Config struct {
 	Services map[string]interface{} `yaml:"services"`
 }
 
+type HeaderSettings struct {
+	Forbid             []string `yaml:"forbid"`
+	PreserveServer     bool     `yaml:"preserveServer"`
+	PreserveXPoweredBy bool     `yaml:"preserveXPoweredBy"`
+	PreserveAltSvc     bool     `yaml:"preserveAltSvc"`
+	PassHost           bool     `yaml:"passHost"`
+	XForward           bool     `yaml:"xForward"`
+}
+
 type Service struct {
 	ServiceID       uuid.UUID
 	ServiceMetadata library.Service
@@ -174,9 +184,15 @@ func logger(next http.Handler) http.Handler {
 func serverChanger(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if !config.Global.Stealth.Enabled {
+			if !strings.Contains("Server", w.Header().Get(":X-Preserve-Headers")) {
 				w.Header().Set("Server", "Fulgens HTTP Server")
+			}
+			if !strings.Contains("X-Powered-By", w.Header().Get(":X-Preserve-Headers")) {
 				w.Header().Set("X-Powered-By", "Go net/http")
-			w.Header().Set("Alt-Svc", "Alt-Svc: h2=\":443\"; ma=3600")
+			}
+			if !strings.Contains("Alt-Svc", w.Header().Get(":X-Preserve-Headers")) {
+				w.Header().Set("Alt-Svc", "h2=\":443\"; ma=3600")
+			}
 		} else {
 			switch config.Global.Stealth.Server {
 			case "nginx":
@@ -196,8 +212,10 @@ func serverChanger(next http.Handler) http.Handler {
 				poweredBy.WriteString("ASP.NET")
 			}
 
+			if poweredBy.Len() > 0 {
 				w.Header().Set("X-Powered-By", poweredBy.String())
 			}
+		}
 		next.ServeHTTP(w, r)
 	})
 }
@@ -377,6 +395,54 @@ func newFileServer(root string, directoryListing bool, path string) http.Handler
 	})
 }
 
+func newReverseProxy(uri *url.URL, headerSettings HeaderSettings) http.Handler {
+	proxy := httputil.NewSingleHostReverseProxy(uri)
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Strip the headers
+		for _, header := range headerSettings.Forbid {
+			r.Header.Del(header)
+		}
+		if !headerSettings.PassHost {
+			r.Host = uri.Host
+		}
+		if !headerSettings.XForward {
+			r.Header["X-Forwarded-For"] = nil
+		} else {
+			r.Header.Set("X-Forwarded-Host", r.Host)
+			if r.URL.Scheme != "" {
+				r.Header.Set("X-Forwarded-Proto", r.URL.Scheme)
+			} else {
+				r.Header.Set("X-Forwarded-Proto", "http")
+			}
+		}
+
+		// Set the preserve headers which will be stripped by the server changer
+		var xPreserveHeaders strings.Builder
+
+		if headerSettings.PreserveServer {
+			xPreserveHeaders.WriteString("Server")
+		}
+
+		if headerSettings.PreserveXPoweredBy {
+			if xPreserveHeaders.Len() > 0 {
+				xPreserveHeaders.WriteString(", ")
+			}
+			xPreserveHeaders.WriteString("X-Powered-By")
+		}
+
+		if headerSettings.PreserveAltSvc {
+			if xPreserveHeaders.Len() > 0 {
+				xPreserveHeaders.WriteString(", ")
+			}
+			xPreserveHeaders.WriteString("Alt-Svc")
+		}
+
+		w.Header().Set(":X-Preserve-Headers", xPreserveHeaders.String())
+
+		proxy.ServeHTTP(w, r)
+	})
+}
+
 func serverError(w http.ResponseWriter, status int) {
 	w.Header().Set("Content-Type", "text/html")
 	w.WriteHeader(status)
@@ -897,17 +963,16 @@ func iterateThroughSubdomains(globalOutbox chan library.InterServiceMessage) {
 					subdomainRouter.Handle(path, http.StripPrefix(rawPath, newFileServer(pathBlock.Static.Root, pathBlock.Static.DirectoryListing, rawPath)))
 					slog.Info("Serving static directory " + pathBlock.Static.Root + " on subdomain " + route.Subdomain + " with pattern " + path)
 				} else if pathBlock.Proxy.URL != "" {
-					// Parse the URL
-					proxyUrl, err := url.Parse(pathBlock.Proxy.URL)
+					// Create the proxy
+					parsedURL, err := url.Parse(pathBlock.Proxy.URL)
 					if err != nil {
 						slog.Error("Error parsing URL: " + err.Error())
 						os.Exit(1)
 					}
-					// Create the proxy
 					if pathBlock.Proxy.StripPrefix {
-						subdomainRouter.Handle(path, http.StripPrefix(strings.TrimSuffix(path, "*"), httputil.NewSingleHostReverseProxy(proxyUrl)))
+						subdomainRouter.Handle(path, http.StripPrefix(strings.TrimSuffix(path, "*"), newReverseProxy(parsedURL, pathBlock.Proxy.Headers)))
 					} else {
-						subdomainRouter.Handle(path, httputil.NewSingleHostReverseProxy(proxyUrl))
+						subdomainRouter.Handle(path, newReverseProxy(parsedURL, pathBlock.Proxy.Headers))
 					}
 				} else if pathBlock.Redirect.URL != "" {
 					// Set the code