[management, reverse proxy] Add reverse proxy feature (#5291)

* implement reverse proxy


---------

Co-authored-by: Alisdair MacLeod <git@alisdairmacleod.co.uk>
Co-authored-by: mlsmaycon <mlsmaycon@gmail.com>
Co-authored-by: Eduard Gert <kontakt@eduardgert.de>
Co-authored-by: Viktor Liu <viktor@netbird.io>
Co-authored-by: Diego Noguês <diego.sure@gmail.com>
Co-authored-by: Diego Noguês <49420+diegocn@users.noreply.github.com>
Co-authored-by: Bethuel Mmbaga <bethuelmbaga12@gmail.com>
Co-authored-by: Zoltan Papp <zoltan.pmail@gmail.com>
Co-authored-by: Ashley Mensah <ashleyamo982@gmail.com>

management/server/http/handlers/proxy/auth.go

@@ -0,0 +1,208 @@
+package proxy
+
+import (
+	"context"
+	"net"
+	"net/http"
+	"net/netip"
+	"net/url"
+	"strings"
+	"time"
+
+	"github.com/coreos/go-oidc/v3/oidc"
+	"github.com/gorilla/mux"
+	log "github.com/sirupsen/logrus"
+	"golang.org/x/oauth2"
+
+	nbgrpc "github.com/netbirdio/netbird/management/internals/shared/grpc"
+	"github.com/netbirdio/netbird/management/server/http/middleware"
+	"github.com/netbirdio/netbird/management/server/types"
+	"github.com/netbirdio/netbird/proxy/auth"
+)
+
+// AuthCallbackHandler handles OAuth callbacks for proxy authentication.
+type AuthCallbackHandler struct {
+	proxyService   *nbgrpc.ProxyServiceServer
+	rateLimiter    *middleware.APIRateLimiter
+	trustedProxies []netip.Prefix
+}
+
+// NewAuthCallbackHandler creates a new OAuth callback handler.
+func NewAuthCallbackHandler(proxyService *nbgrpc.ProxyServiceServer, trustedProxies []netip.Prefix) *AuthCallbackHandler {
+	rateLimiterConfig := &middleware.RateLimiterConfig{
+		RequestsPerMinute: 10,
+		Burst:             15,
+		CleanupInterval:   5 * time.Minute,
+		LimiterTTL:        10 * time.Minute,
+	}
+
+	return &AuthCallbackHandler{
+		proxyService:   proxyService,
+		rateLimiter:    middleware.NewAPIRateLimiter(rateLimiterConfig),
+		trustedProxies: trustedProxies,
+	}
+}
+
+// RegisterEndpoints registers the OAuth callback endpoint.
+func (h *AuthCallbackHandler) RegisterEndpoints(router *mux.Router) {
+	router.HandleFunc(types.ProxyCallbackEndpoint, h.handleCallback).Methods(http.MethodGet)
+}
+
+func (h *AuthCallbackHandler) handleCallback(w http.ResponseWriter, r *http.Request) {
+	clientIP := h.resolveClientIP(r)
+	if !h.rateLimiter.Allow(clientIP) {
+		log.WithField("client_ip", clientIP).Warn("OAuth callback rate limit exceeded")
+		http.Error(w, "Too many requests. Please try again later.", http.StatusTooManyRequests)
+		return
+	}
+
+	state := r.URL.Query().Get("state")
+
+	codeVerifier, originalURL, err := h.proxyService.ValidateState(state)
+	if err != nil {
+		log.WithError(err).Error("OAuth callback state validation failed")
+		http.Error(w, "Invalid state parameter", http.StatusBadRequest)
+		return
+	}
+
+	redirectURL, err := url.Parse(originalURL)
+	if err != nil {
+		log.WithError(err).Error("Failed to parse redirect URL")
+		http.Error(w, "Invalid redirect URL", http.StatusBadRequest)
+		return
+	}
+
+	oidcConfig := h.proxyService.GetOIDCConfig()
+
+	provider, err := oidc.NewProvider(r.Context(), oidcConfig.Issuer)
+	if err != nil {
+		log.WithError(err).Error("Failed to create OIDC provider")
+		http.Error(w, "Failed to create OIDC provider", http.StatusInternalServerError)
+		return
+	}
+
+	token, err := (&oauth2.Config{
+		ClientID:    oidcConfig.ClientID,
+		Endpoint:    provider.Endpoint(),
+		RedirectURL: oidcConfig.CallbackURL,
+	}).Exchange(r.Context(), r.URL.Query().Get("code"), oauth2.VerifierOption(codeVerifier))
+	if err != nil {
+		log.WithError(err).Error("Failed to exchange code for token")
+		http.Error(w, "Failed to exchange code for token", http.StatusInternalServerError)
+		return
+	}
+
+	userID := extractUserIDFromToken(r.Context(), provider, oidcConfig, token)
+	if userID == "" {
+		log.Error("Failed to extract user ID from OIDC token")
+		http.Error(w, "Failed to validate token", http.StatusUnauthorized)
+		return
+	}
+
+	// Group validation is performed by the proxy via ValidateSession gRPC call.
+	// This allows the proxy to show 403 pages directly without redirect dance.
+
+	sessionToken, err := h.proxyService.GenerateSessionToken(r.Context(), redirectURL.Hostname(), userID, auth.MethodOIDC)
+	if err != nil {
+		log.WithError(err).Error("Failed to create session token")
+		redirectURL.Scheme = "https"
+		query := redirectURL.Query()
+		query.Set("error", "access_denied")
+		query.Set("error_description", "Service configuration error")
+		redirectURL.RawQuery = query.Encode()
+		http.Redirect(w, r, redirectURL.String(), http.StatusFound)
+		return
+	}
+
+	redirectURL.Scheme = "https"
+
+	query := redirectURL.Query()
+	query.Set("session_token", sessionToken)
+	redirectURL.RawQuery = query.Encode()
+
+	log.WithField("redirect", redirectURL.Host).Debug("OAuth callback: redirecting user with session token")
+	http.Redirect(w, r, redirectURL.String(), http.StatusFound)
+}
+
+func extractUserIDFromToken(ctx context.Context, provider *oidc.Provider, config nbgrpc.ProxyOIDCConfig, token *oauth2.Token) string {
+	rawIDToken, ok := token.Extra("id_token").(string)
+	if !ok {
+		log.Warn("No id_token in OIDC response")
+		return ""
+	}
+
+	verifier := provider.Verifier(&oidc.Config{
+		ClientID: config.ClientID,
+	})
+
+	idToken, err := verifier.Verify(ctx, rawIDToken)
+	if err != nil {
+		log.WithError(err).Warn("Failed to verify ID token")
+		return ""
+	}
+
+	var claims struct {
+		Subject string `json:"sub"`
+	}
+	if err := idToken.Claims(&claims); err != nil {
+		log.WithError(err).Warn("Failed to extract claims from ID token")
+		return ""
+	}
+
+	return claims.Subject
+}
+
+// resolveClientIP extracts the real client IP from the request.
+// When trustedProxies is non-empty and the direct peer is trusted,
+// it walks X-Forwarded-For right-to-left skipping trusted IPs.
+// Otherwise it returns RemoteAddr directly.
+func (h *AuthCallbackHandler) resolveClientIP(r *http.Request) string {
+	remoteIP := extractHost(r.RemoteAddr)
+
+	if len(h.trustedProxies) == 0 || !isTrustedProxy(remoteIP, h.trustedProxies) {
+		return remoteIP
+	}
+
+	xff := r.Header.Get("X-Forwarded-For")
+	if xff == "" {
+		return remoteIP
+	}
+
+	parts := strings.Split(xff, ",")
+	for i := len(parts) - 1; i >= 0; i-- {
+		ip := strings.TrimSpace(parts[i])
+		if ip == "" {
+			continue
+		}
+		if !isTrustedProxy(ip, h.trustedProxies) {
+			return ip
+		}
+	}
+
+	// All IPs in XFF are trusted; return the leftmost as best guess.
+	if first := strings.TrimSpace(parts[0]); first != "" {
+		return first
+	}
+	return remoteIP
+}
+
+func extractHost(remoteAddr string) string {
+	host, _, err := net.SplitHostPort(remoteAddr)
+	if err != nil {
+		return remoteAddr
+	}
+	return host
+}
+
+func isTrustedProxy(ipStr string, trusted []netip.Prefix) bool {
+	addr, err := netip.ParseAddr(ipStr)
+	if err != nil {
+		return false
+	}
+	for _, prefix := range trusted {
+		if prefix.Contains(addr) {
+			return true
+		}
+	}
+	return false
+}