HTTP proxy authentication fixes (#300)

- Only accepts HTTP 1.x protocols
- Only checks the credentials when the method is `CONNECT` or the request URL is absolute
- More logging on authorization failures
- Removes the authorization headers before forwarding the HTTP(s) requests
- Refers to #298

internal/httpproxy/accept.go

@@ -0,0 +1,24 @@
+package httpproxy
+
+import (
+	"fmt"
+	"net/http"
+)
+
+func (h *handler) isAccepted(responseWriter http.ResponseWriter, request *http.Request) bool {
+	// Not compatible with HTTP < 1.0 or HTTP >= 2.0 (see https://github.com/golang/go/issues/14797#issuecomment-196103814)
+	const (
+		minimalMajorVersion = 1
+		minimalMinorVersion = 0
+		maximumMajorVersion = 2
+		maximumMinorVersion = 0
+	)
+	if !request.ProtoAtLeast(minimalMajorVersion, minimalMinorVersion) ||
+		request.ProtoAtLeast(maximumMajorVersion, maximumMinorVersion) {
+		message := fmt.Sprintf("http version not supported: %s", request.Proto)
+		h.logger.Info("%s, from %s", message, request.RemoteAddr)
+		http.Error(responseWriter, message, http.StatusBadRequest)
+		return false
+	}
+	return true
+}

internal/httpproxy/auth.go

@@ -6,10 +6,13 @@ import (
 	"strings"
 )
 
-func isAuthorized(responseWriter http.ResponseWriter, request *http.Request,
-	username, password string) (authorized bool) {
+func (h *handler) isAuthorized(responseWriter http.ResponseWriter, request *http.Request) (authorized bool) {
+	if len(h.username) == 0 || (request.Method != "CONNECT" && !request.URL.IsAbs()) {
+		return true
+	}
 	basicAuth := request.Header.Get("Proxy-Authorization")
 	if len(basicAuth) == 0 {
+		h.logger.Info("Proxy-Authorization header not found from %s", request.RemoteAddr)
 		responseWriter.Header().Set("Proxy-Authenticate", `Basic realm="Access to Gluetun over HTTP"`)
 		responseWriter.WriteHeader(http.StatusProxyAuthRequired)
 		return false
@@ -17,6 +20,8 @@ func isAuthorized(responseWriter http.ResponseWriter, request *http.Request,
 	b64UsernamePassword := strings.TrimPrefix(basicAuth, "Basic ")
 	b, err := base64.StdEncoding.DecodeString(b64UsernamePassword)
 	if err != nil {
+		h.logger.Info("Cannot decode Proxy-Authorization header value from %s: %s",
+			request.RemoteAddr, err.Error())
 		responseWriter.WriteHeader(http.StatusUnauthorized)
 		return false
 	}
@@ -26,7 +31,9 @@ func isAuthorized(responseWriter http.ResponseWriter, request *http.Request,
 		responseWriter.WriteHeader(http.StatusBadRequest)
 		return false
 	}
-	if username != usernamePassword[0] && password != usernamePassword[1] {
+	if h.username != usernamePassword[0] || h.password != usernamePassword[1] {
+		h.logger.Info("Username or password mismatch from %s", request.RemoteAddr)
+		h.logger.Debug("username provided %q and password provided %q", usernamePassword[0], usernamePassword[1])
 		responseWriter.WriteHeader(http.StatusUnauthorized)
 		return false
 	}

internal/httpproxy/handler.go

@@ -34,10 +34,15 @@ type handler struct {
 }
 
 func (h *handler) ServeHTTP(responseWriter http.ResponseWriter, request *http.Request) {
-	if len(h.username) > 0 && !isAuthorized(responseWriter, request, h.username, h.password) {
-		h.logger.Info("%s unauthorized", request.RemoteAddr)
+	if !h.isAccepted(responseWriter, request) {
 		return
 	}
+	if !h.isAuthorized(responseWriter, request) {
+		return
+	}
+	request.Header.Del("Proxy-Connection")
+	request.Header.Del("Proxy-Authenticate")
+	request.Header.Del("Proxy-Authorization")
 	switch request.Method {
 	case http.MethodConnect:
 		h.handleHTTPS(responseWriter, request)