traefikoidc/url_helpers.go

// Package traefikoidc provides OIDC authentication middleware for Traefik.
// This file contains URL-related helper methods for building, validating, and processing URLs
// used in the OIDC authentication flow.
package traefikoidc

import (
	"fmt"
	"net"
	"net/url"
	"strings"
)

// determineExcludedURL checks if a URL path should bypass OIDC authentication.
// It compares the request path against configured excluded URL prefixes.
// Parameters:
//   - currentRequest: The request path to check.
//
// Returns:
//   - true if the URL should be excluded from authentication, false otherwise.
func (t *TraefikOidc) determineExcludedURL(currentRequest string) bool {
	for excludedURL := range t.excludedURLs {
		if pathExcluded(currentRequest, excludedURL) {
			t.logger.Debugf("URL is excluded - got %s / excluded hit: %s", currentRequest, excludedURL)
			return true
		}
	}
	return false
}

// pathExcluded reports whether requestPath is covered by an excluded prefix at a
// natural boundary: an exact match, a sub-path ("/public" → "/public/x"), or a
// file extension ("/favicon" → "/favicon.ico"). It deliberately does NOT match
// an unrelated sibling such as "/publicsecret", so a configured exclusion can no
// longer be widened into an authentication bypass on a different resource.
func pathExcluded(requestPath, excluded string) bool {
	excluded = strings.TrimRight(excluded, "/")
	if excluded == "" {
		// A "/" (root) exclusion only matches the root path, not everything.
		return requestPath == "" || requestPath == "/"
	}
	if requestPath == excluded {
		return true
	}
	if !strings.HasPrefix(requestPath, excluded) {
		return false
	}
	switch requestPath[len(excluded)] {
	case '/', '.':
		return true
	default:
		return false
	}
}

// buildAuthURL constructs the OIDC provider authorization URL.
// It builds the URL with all necessary parameters including client_id, scopes,
// PKCE parameters, and provider-specific parameters for Google and Azure.
// Parameters:
//   - redirectURL: The callback URL for after authentication.
//   - state: The CSRF token for state validation.
//   - nonce: The nonce for replay protection.
//   - codeChallenge: The PKCE code challenge (if PKCE is enabled).
//
// Returns:
//   - The fully constructed authorization URL string.
func (t *TraefikOidc) buildAuthURL(redirectURL, state, nonce, codeChallenge string) string {
	params := url.Values{}
	params.Set("client_id", t.clientID)
	params.Set("response_type", "code")
	params.Set("redirect_uri", redirectURL)
	params.Set("state", state)
	params.Set("nonce", nonce)

	// Non-standard `audience` param for custom API audiences (e.g. Auth0).
	// Keyed on explicitAudience, not audience — see TraefikOidc.explicitAudience.
	// Only add if configured and different from client_id; ID tokens always
	// have aud=client_id per OIDC spec.
	if t.explicitAudience != "" && t.explicitAudience != t.clientID {
		params.Set("audience", t.explicitAudience)
		t.logger.Debugf("Adding audience parameter to authorize URL: %s", t.explicitAudience)
	}

	// RFC 8707 resource indicator — see Config.Resource. Runs before
	// extraAuthParams so an operator-configured "resource" key there cannot
	// override or duplicate it.
	if t.resource != "" {
		params.Set("resource", t.resource)
		t.logger.Debugf("Adding resource parameter to authorize URL: %s", t.resource)
	}

	if t.enablePKCE && codeChallenge != "" {
		params.Set("code_challenge", codeChallenge)
		params.Set("code_challenge_method", "S256")
	}

	scopes := make([]string, len(t.scopes))
	copy(scopes, t.scopes)

	// Apply discovery-based scope filtering if available
	// Read scopesSupported with RLock
	t.metadataMu.RLock()
	scopesSupported := t.scopesSupported
	t.metadataMu.RUnlock()

	if t.scopeFilter != nil && len(scopesSupported) > 0 {
		scopes = t.scopeFilter.FilterSupportedScopes(scopes, scopesSupported, t.providerURL)
		t.logger.Debugf("TraefikOidc.buildAuthURL: After discovery filtering: %v", scopes)
	}

	// Then apply provider-specific modifications
	if t.isGoogleProvider() {
		// Google: Remove offline_access if present, add access_type=offline
		filteredScopes := make([]string, 0, len(scopes))
		for _, scope := range scopes {
			if scope != "offline_access" {
				filteredScopes = append(filteredScopes, scope)
			}
		}
		scopes = filteredScopes

		params.Set("access_type", "offline")
		t.logger.Debug("Google OIDC provider detected, added access_type=offline for refresh tokens")

		params.Set("prompt", "consent")
		t.logger.Debug("Google OIDC provider detected, added prompt=consent to ensure refresh tokens")
	} else if t.isAzureProvider() {
		params.Set("response_mode", "query")
		t.logger.Debug("Azure AD provider detected, added response_mode=query")

		hasOfflineAccess := false

		for _, scope := range scopes {
			if scope == "offline_access" {
				hasOfflineAccess = true
				break
			}
		}

		if !t.overrideScopes || (t.overrideScopes && len(t.scopes) == 0) {
			if !hasOfflineAccess {
				scopes = append(scopes, "offline_access")
				t.logger.Debugf("Azure AD provider: Added offline_access scope (overrideScopes: %t, user scopes count: %d)", t.overrideScopes, len(t.scopes))
			}
		} else {
			t.logger.Debugf("Azure AD provider: User is overriding scopes (count: %d), offline_access not automatically added.", len(t.scopes))
		}
	} else {
		if !t.overrideScopes || (t.overrideScopes && len(t.scopes) == 0) {
			hasOfflineAccess := false
			for _, scope := range scopes {
				if scope == "offline_access" {
					hasOfflineAccess = true
					break
				}
			}
			if !hasOfflineAccess {
				scopes = append(scopes, "offline_access")
				t.logger.Debugf("Standard provider: Added offline_access scope (overrideScopes: %t, user scopes count: %d)", t.overrideScopes, len(t.scopes))
			}
		} else {
			t.logger.Debugf("Standard provider: User is overriding scopes (count: %d), offline_access not automatically added.", len(t.scopes))
		}
	}

	// Final filtering pass to remove anything the provider doesn't support
	// Read scopesSupported with RLock
	t.metadataMu.RLock()
	scopesSupported = t.scopesSupported
	t.metadataMu.RUnlock()

	if t.scopeFilter != nil && len(scopesSupported) > 0 {
		scopes = t.scopeFilter.FilterSupportedScopes(scopes, scopesSupported, t.providerURL)
		t.logger.Debugf("TraefikOidc.buildAuthURL: After final filtering: %v", scopes)
	}

	if len(scopes) > 0 {
		finalScopeString := strings.Join(scopes, " ")
		params.Set("scope", finalScopeString)
		t.logger.Debugf("TraefikOidc.buildAuthURL: Final scope string being sent to OIDC provider: %s", finalScopeString)
	}

	// Apply operator-configured extra authorization parameters (e.g.
	// screen_hint, login_hint, ui_locales, prompt). These are added last but
	// can never override parameters the plugin itself manages (client_id,
	// state, nonce, redirect_uri, code_challenge, scope, response_type, ...):
	// a key already present in params is left untouched, so this cannot
	// weaken security-critical parameters.
	for key, value := range t.extraAuthParams {
		if params.Get(key) == "" {
			params.Set(key, value)
			t.logger.Debugf("TraefikOidc.buildAuthURL: Added extra auth param %s", key)
		} else {
			t.logger.Debugf("TraefikOidc.buildAuthURL: Skipped extra auth param %s (already set by plugin)", key)
		}
	}

	// Read authURL with RLock
	t.metadataMu.RLock()
	authURL := t.authURL
	t.metadataMu.RUnlock()

	return t.buildURLWithParams(authURL, params)
}

// buildURLWithParams constructs a URL by combining a base URL with query parameters.
// It handles both relative and absolute URLs, validates URL security,
// and properly encodes query parameters.
// Parameters:
//   - baseURL: The base URL to append parameters to.
//   - params: The query parameters to append.
//
// Returns:
//   - The fully constructed URL string with appended query parameters.
func (t *TraefikOidc) buildURLWithParams(baseURL string, params url.Values) string {
	if baseURL != "" {
		if strings.HasPrefix(baseURL, "http://") || strings.HasPrefix(baseURL, "https://") {
			if err := t.validateURL(baseURL); err != nil {
				t.logger.Errorf("URL validation failed for %s: %v", baseURL, err)
				return ""
			}
		}
	}

	if !strings.HasPrefix(baseURL, "http://") && !strings.HasPrefix(baseURL, "https://") {
		// Read issuerURL with RLock
		t.metadataMu.RLock()
		issuerURL := t.issuerURL
		t.metadataMu.RUnlock()

		issuerURLParsed, err := url.Parse(issuerURL)
		if err != nil {
			t.logger.Errorf("Could not parse issuerURL: %s. Error: %v", issuerURL, err)
			return ""
		}

		baseURLParsed, err := url.Parse(baseURL)
		if err != nil {
			t.logger.Errorf("Could not parse baseURL: %s. Error: %v", baseURL, err)
			return ""
		}

		resolvedURL := issuerURLParsed.ResolveReference(baseURLParsed)

		if err := t.validateURL(resolvedURL.String()); err != nil {
			t.logger.Errorf("Resolved URL validation failed for %s: %v", resolvedURL.String(), err)
			return ""
		}

		resolvedURL.RawQuery = params.Encode()
		return resolvedURL.String()
	}

	u, err := url.Parse(baseURL)
	if err != nil {
		t.logger.Errorf("Could not parse absolute baseURL: %s. Error: %v", baseURL, err)
		return ""
	}

	if err := t.validateParsedURL(u); err != nil {
		t.logger.Errorf("Parsed URL validation failed for %s: %v", baseURL, err)
		return ""
	}

	u.RawQuery = params.Encode()
	return u.String()
}

// validateURL performs security validation on URLs to prevent SSRF attacks.
// It checks for allowed schemes, validates hosts, and prevents access to private networks.
// Parameters:
//   - urlStr: The URL string to validate.
//
// Returns:
//   - An error if the URL is invalid or poses security risks, nil if valid.
func (t *TraefikOidc) validateURL(urlStr string) error {
	if urlStr == "" {
		return fmt.Errorf("empty URL")
	}

	u, err := url.Parse(urlStr)
	if err != nil {
		return fmt.Errorf("invalid URL format: %w", err)
	}

	return t.validateParsedURL(u)
}

// validateParsedURL validates a parsed URL structure for security.
// It checks schemes, hosts, and paths to prevent malicious URLs.
// Parameters:
//   - u: The parsed URL to validate.
//
// Returns:
//   - An error if the URL is invalid or dangerous, nil if safe.
func (t *TraefikOidc) validateParsedURL(u *url.URL) error {
	allowedSchemes := map[string]bool{
		"https": true,
		"http":  true,
	}

	if !allowedSchemes[u.Scheme] {
		return fmt.Errorf("disallowed URL scheme: %s", u.Scheme)
	}

	if u.Scheme == "http" {
		t.logger.Debugf("Warning: Using HTTP scheme for URL: %s", u.String())
	}

	if u.Host == "" {
		return fmt.Errorf("missing host in URL")
	}

	if err := t.validateHost(u.Host); err != nil {
		return fmt.Errorf("invalid host: %w", err)
	}

	if strings.Contains(u.Path, "..") {
		return fmt.Errorf("path traversal detected in URL path")
	}

	return nil
}

// validateDiscoveredEndpoint validates an endpoint URL obtained from the
// provider's OIDC/OAuth2 discovery document before the plugin issues any
// outbound request to it. A discovery document is attacker-influenced if the
// provider is malicious or its TLS is broken, so an unvalidated endpoint is an
// SSRF vector (e.g. jwks_uri or introspection_endpoint pointed at the cloud
// metadata service 169.254.169.254 or an internal host).
//
// Empty endpoints are allowed (they are optional). Link-local (which covers the
// 169.254.0.0/16 metadata range), multicast and unspecified addresses are
// always rejected. Private addresses are rejected unless allowPrivateIPAddresses
// is set. Loopback is rejected unless allowLoopback is true — which the caller
// sets only when the operator-configured providerURL is itself loopback (local
// development, in-cluster sidecars, tests), so production deployments pointed at
// a real provider still block loopback SSRF.
func (t *TraefikOidc) validateDiscoveredEndpoint(urlStr string, allowLoopback bool) error {
	if urlStr == "" {
		return nil
	}
	u, err := url.Parse(urlStr)
	if err != nil {
		return fmt.Errorf("invalid URL format: %w", err)
	}
	if u.Scheme != "https" && u.Scheme != "http" {
		return fmt.Errorf("disallowed URL scheme: %q", u.Scheme)
	}
	if u.Host == "" {
		return fmt.Errorf("missing host in URL")
	}
	if ip := net.ParseIP(u.Hostname()); ip != nil {
		switch {
		case ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() || ip.IsMulticast() || ip.IsUnspecified():
			return fmt.Errorf("endpoint host is a blocked address: %s", ip)
		case ip.IsLoopback() && !allowLoopback:
			return fmt.Errorf("endpoint host is a loopback address: %s", ip)
		case ip.IsPrivate() && !t.allowPrivateIPAddresses:
			return fmt.Errorf("endpoint host is a private address: %s", ip)
		}
	}
	if strings.Contains(u.Path, "..") {
		return fmt.Errorf("path traversal detected in URL path")
	}
	return nil
}

// sameHost reports whether two URLs share the same host:port (case-insensitive).
// Used to pin the credential-bearing introspection endpoint to the operator-
// configured provider so a poisoned discovery document cannot redirect the
// client secret to an attacker-controlled host.
func sameHost(a, b string) bool {
	ua, erra := url.Parse(a)
	ub, errb := url.Parse(b)
	if erra != nil || errb != nil || ua.Host == "" || ub.Host == "" {
		return false
	}
	return strings.EqualFold(ua.Host, ub.Host)
}

// validateHost validates a hostname or IP address for security.
// It prevents access to localhost, private networks, and known metadata endpoints.
// When allowPrivateIPAddresses is enabled, private IP checks are skipped.
// Parameters:
//   - host: The host string to validate (may include port).
//
// Returns:
//   - An error if the host is dangerous or not allowed, nil if safe.
func (t *TraefikOidc) validateHost(host string) error {
	hostname := host
	if strings.Contains(host, ":") {
		var err error
		hostname, _, err = net.SplitHostPort(host)
		if err != nil {
			return fmt.Errorf("invalid host format: %w", err)
		}
	}

	ip := net.ParseIP(hostname)
	if ip != nil {
		// Loopback addresses are blocked by default, but allowed when the
		// plugin was constructed with a loopback providerURL (local
		// development) — see allowLoopbackHosts.
		if ip.IsLoopback() && !t.allowLoopbackHosts {
			return fmt.Errorf("access to loopback/link-local IP addresses is not allowed: %s", ip.String())
		}

		// Link-local and multicast addresses are always blocked.
		if ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast() {
			return fmt.Errorf("access to loopback/link-local IP addresses is not allowed: %s", ip.String())
		}

		// Skip private IP check if allowPrivateIPAddresses is enabled
		if !t.allowPrivateIPAddresses && ip.IsPrivate() {
			return fmt.Errorf("access to private/internal IP addresses is not allowed: %s", ip.String())
		}

		if ip.IsUnspecified() || ip.IsMulticast() {
			return fmt.Errorf("access to unspecified or multicast IP addresses is not allowed: %s", ip.String())
		}
	}

	// Always blocked regardless of allowLoopbackHosts: these have no IP-branch
	// backstop (net.ParseIP returns nil for hostnames), so bypassing them
	// would open an SSRF path to the cloud metadata service.
	alwaysDangerousHosts := map[string]bool{
		"0.0.0.0":                  true,
		"169.254.169.254":          true,
		"metadata.google.internal": true,
	}

	if alwaysDangerousHosts[strings.ToLower(hostname)] {
		return fmt.Errorf("access to dangerous hostname is not allowed: %s", hostname)
	}

	// localhost/loopback literals are blocked unless allowLoopbackHosts
	// permits them (see allowLoopbackHosts doc comment on TraefikOidc).
	if !t.allowLoopbackHosts && isLoopbackHost(hostname) {
		return fmt.Errorf("access to dangerous hostname is not allowed: %s", hostname)
	}

	return nil
}