fix(security): constant-time token compare, validate OIDC port param (#25, #26) (#45)

Issue #25 — timing attack in static token comparison:
Both token comparison sites in proxy.go used Go's == operator which is not
constant-time. An attacker measuring response latency could determine the
correct token one byte at a time.
Fix: replace == with crypto/subtle.ConstantTimeCompare at both call sites.

Issue #26 — port parameter not validated in OIDC authorize endpoint:
The 'p' query parameter was interpolated directly into the redirect URL
(http://127.0.0.1:%s/callback) without any validation, allowing path
injection via values like '80/evil-path#'.
Fix: parse port with strconv.Atoi and reject values outside [1, 65535].
Use %d (not %s) in the format string to prevent any further injection.

Co-authored-by: Mangirdas Judeikis <mjudeikis@gmail.com>
Co-authored-by: Mangirdas Judeikis <mangirdas@judeikis.lt>

Author: 3 people

pkg/server/auth/handler.go

@@ -26,6 +26,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"net/http"
+	"strconv"
 
 	oidc "github.com/coreos/go-oidc"
 	"github.com/gorilla/mux"
@@ -104,8 +105,16 @@ func (h *Handler) HandleAuthorize(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// Validate port is a number in [1, 65535] to prevent path injection
+	// into the redirect URL (fix for #26).
+	portNum, err := strconv.Atoi(port)
+	if err != nil || portNum < 1 || portNum > 65535 {
+		http.Error(w, "invalid port parameter: must be a number between 1 and 65535", http.StatusBadRequest)
+		return
+	}
+
 	authCode := tenancyv1alpha1.AuthCode{
-		RedirectURL: fmt.Sprintf("http://127.0.0.1:%s/callback", port),
+		RedirectURL: fmt.Sprintf("http://127.0.0.1:%d/callback", portNum),
 		SessionID:   sessionID,
 	}
 

pkg/server/proxy/proxy.go

@@ -20,6 +20,7 @@ package proxy
 import (
 	"context"
 	"crypto/sha256"
+	"crypto/subtle"
 	"crypto/tls"
 	"encoding/base64"
 	"encoding/hex"
@@ -123,8 +124,9 @@ func (p *KCPProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	token := strings.TrimPrefix(authHeader, "Bearer ")
 
 	// Static token: create user/workspace if needed and proxy to user's workspace.
+	// Use constant-time comparison to prevent timing side-channel attacks.
 	for _, staticToken := range p.staticAuthTokens {
-		if staticToken != "" && token == staticToken {
+		if staticToken != "" && subtle.ConstantTimeCompare([]byte(token), []byte(staticToken)) == 1 {
 			p.serveStaticToken(w, r, token)
 			return
 		}
@@ -541,9 +543,10 @@ func (p *KCPProxy) HandleTokenLogin(w http.ResponseWriter, r *http.Request) {
 	token := strings.TrimPrefix(authHeader, "Bearer ")
 
 	// Validate token against static tokens.
+	// Use constant-time comparison to prevent timing side-channel attacks.
 	validToken := false
 	for _, staticToken := range p.staticAuthTokens {
-		if staticToken != "" && token == staticToken {
+		if staticToken != "" && subtle.ConstantTimeCompare([]byte(token), []byte(staticToken)) == 1 {
 			validToken = true
 			break
 		}