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fix: harden cookie-less sso token redirects #1087

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fix: harden cookie-less sso token redirects #1087

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259 changes: 187 additions & 72 deletions inc/sso/class-sso.php
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Original file line number Diff line number Diff line change
Expand Up @@ -261,6 +261,8 @@ public function startup(): void {
*/
add_filter('determine_current_user', [$this, 'determine_current_user'], 90);

add_action('init', [$this, 'handle_cookie_less_sso_token'], 4);

add_action('init', [$this, 'convert_bearer_into_auth_cookies']);

add_filter('removable_query_args', [$this, 'add_sso_removable_query_args']);
Expand All @@ -274,6 +276,9 @@ public function startup(): void {
// If user is already logged in and visiting login page with SSO params, redirect to subsite.
add_action('login_init', [$this, 'handle_already_logged_in_on_login_page']);

// Custom login pages (e.g. /login/) do not fire login_init.
add_action('template_redirect', [$this, 'handle_already_logged_in_on_login_page'], 1);

/**
* Adds the SSO scripts to the head of the front-end
* and the login page to try to perform a SSO flow.
Expand Down Expand Up @@ -512,7 +517,7 @@ public function handle_server($response_type = 'redirect'): void {
*/
private function handle_main_site_logged_in_user($response_type): void {

$return_url = $this->input('return_url', get_home_url());
$return_url = $this->get_sso_return_url(get_home_url());
$redirect_to = $this->input('redirect_to', admin_url());

// If user is logged in, redirect back to the subsite with verification.
Expand All @@ -535,11 +540,8 @@ private function handle_main_site_logged_in_user($response_type): void {
exit;
}

// Redirect back to the subsite with verification code.
$url = add_query_arg([
'sso_verify' => $verification_code,
'redirect_to' => $redirect_to,
], $return_url);
$url = $this->add_cookie_less_sso_token($return_url, get_current_user_id());
$url = add_query_arg('redirect_to', $redirect_to, $url);

wp_safe_redirect($url, 302, 'WP-Ultimo-SSO');
exit;
Expand All @@ -562,72 +564,206 @@ public function handle_login_redirect($redirect_to, $requested_redirect_to, $use
return $redirect_to;
}

// Check if this is part of an SSO flow (we have return_url or already came from subsite).
$return_url = $this->input('return_url', '');
$return_url = $this->get_sso_return_url($redirect_to);

if ( ! empty($return_url) ) {
return $this->add_cookie_less_sso_token($return_url, $user->ID);
}

// Default: send to the subsite dashboard or main site admin.
return $redirect_to;
}

/**
* Generate a time-limited SSO token for cookie-less authentication.
*
* @since 2.0.11
*
* @param int $user_id User ID.
* @param string $audience Token audience URL.
* @return string The token.
*/
private function generate_sso_token(int $user_id, string $audience): string {
$audience_host = strtolower((string) wp_parse_url($audience, PHP_URL_HOST));

// Token expires in 5 minutes.
$expiry = time() + 300;
$jti = wp_generate_uuid4();

$payload = wp_json_encode([
'user_id' => $user_id,
'exp' => $expiry,
'aud' => $audience_host,
'jti' => $jti,
]);

set_site_transient('wu_sso_magic_' . $jti, 1, 300);

// HMAC-signed token.
$hmac = hash_hmac('sha256', $payload, wp_salt('auth'));

return rtrim(strtr(base64_encode($hmac . '::' . $payload), '+/', '-_'), '=');
}

/**
* Add a cookie-less SSO token to a cross-domain URL.
*
* @since 2.0.11
*
* @param string $url URL to decorate.
* @param int $user_id User ID.
* @return string
*/
private function add_cookie_less_sso_token(string $url, int $user_id): string {
if ( ! $this->is_cross_domain_url($url) || $user_id <= 0 ) {
return $url;
}

return add_query_arg('wu_sso_token', $this->generate_sso_token($user_id, $url), $url);
}

/**
* Return the SSO return URL from request params or a direct redirect_to URL.
*
* @since 2.0.11
*
* @param string $fallback Fallback URL.
* @return string
*/
private function get_sso_return_url(string $fallback = ''): string {
$return_url = $this->input('return_url', '');
$redirect_to = $this->input('redirect_to', $fallback);

if ( ! empty($redirect_to) && $this->is_cross_domain_url($redirect_to) ) {
return esc_url_raw($redirect_to);
}

// Also extract return_url from redirect_to if it's encoded as a query param
if ( empty($return_url) && ! empty($redirect_to) ) {
$parsed = wp_parse_url($redirect_to, PHP_URL_QUERY);

if ( $parsed ) {
parse_str($parsed, $query_params);

if ( ! empty($query_params['return_url']) ) {
$return_url = $query_params['return_url'];
}
}
}

if ( ! empty($return_url) ) {
// Check if redirecting to a different domain (needs magic token for cookie-less auth)
$return_host = wp_parse_url($return_url, PHP_URL_HOST);
$main_host = wp_parse_url(get_site_url(), PHP_URL_HOST);

if ( $return_host && $return_host !== $main_host ) {
// Generate a time-limited magic token for cookie-less authentication
$token = $this->generate_sso_token($user->ID);
$return_url = add_query_arg('wu_sso_token', $token, $return_url);
}
return esc_url_raw($return_url ?: $fallback);
}

/**
* Validate and consume a cookie-less SSO token on the target site.
*
* @since 2.0.11
* @return void
*/
public function handle_cookie_less_sso_token(): void {
$token = $this->input('wu_sso_token', '');

// Get the subsite URL and redirect there.
return $return_url;
if ( empty($token) ) {
return;
}

// If redirect_to points to a subsite (different domain), use that.
if ( ! empty($redirect_to) && wu_is_same_domain() === false ) {
// Generate magic token for cross-domain redirect
$redirect_host = wp_parse_url($redirect_to, PHP_URL_HOST);
$main_host = wp_parse_url(get_site_url(), PHP_URL_HOST);
$result = $this->validate_sso_token($token);

if ( $redirect_host && $redirect_host !== $main_host ) {
$token = $this->generate_sso_token($user->ID);
$redirect_to = add_query_arg('wu_sso_token', $token, $redirect_to);
}
if ( is_wp_error($result) ) {
wu_log_add(self::LOG_FILE_NAME, $result->get_error_message(), LogLevel::ERROR);
return;
}

return $redirect_to;
$user_id = (int) $result['user_id'];

wp_set_auth_cookie($user_id, true);
wp_set_current_user($user_id);

$redirect_to = $this->input('redirect_to', admin_url());
$redirect_to = remove_query_arg('wu_sso_token', $redirect_to);

wp_safe_redirect(wp_validate_redirect($redirect_to, admin_url()), 302, 'WP-Ultimo-SSO');
exit;
}

/**
* Validate a cookie-less SSO token.
*
* @since 2.0.11
*
* @param string $token Token to validate.
* @return array|\WP_Error
*/
private function validate_sso_token(string $token) {
$token = strtr($token, '-_', '+/');
$padding = strlen($token) % 4;

if ( $padding ) {
$token .= str_repeat('=', 4 - $padding);
}

// Default: send to the subsite dashboard or main site admin.
return $redirect_to;
$decoded = base64_decode($token, true);

if ( ! $decoded || false === strpos($decoded, '::') ) {
return new \WP_Error('invalid_token', __('Invalid SSO token format.', 'ultimate-multisite'));
}

[$expected_hmac, $payload_json] = explode('::', $decoded, 2);
$hmac = hash_hmac('sha256', $payload_json, wp_salt('auth'));

if ( ! hash_equals($hmac, $expected_hmac) ) {
return new \WP_Error('invalid_signature', __('Invalid SSO token signature.', 'ultimate-multisite'));
}

$payload = json_decode($payload_json, true);

if ( json_last_error() !== JSON_ERROR_NONE ) {
return new \WP_Error('invalid_payload', __('Invalid SSO token payload.', 'ultimate-multisite'));
}

if ( empty($payload['exp']) || $payload['exp'] < time() ) {
return new \WP_Error('token_expired', __('SSO token has expired.', 'ultimate-multisite'));
}

$current_host = strtolower((string) wp_parse_url(home_url(), PHP_URL_HOST));
$audience = strtolower((string) ($payload['aud'] ?? ''));

if ( empty($audience) || $audience !== $current_host ) {
return new \WP_Error('invalid_audience', __('Invalid SSO token audience.', 'ultimate-multisite'));
}

$jti = (string) ($payload['jti'] ?? '');

if ( empty($jti) || ! get_site_transient('wu_sso_magic_' . $jti) ) {
return new \WP_Error('invalid_token', __('SSO token has already been used or is invalid.', 'ultimate-multisite'));
}

delete_site_transient('wu_sso_magic_' . $jti);

$user = get_user_by('id', (int) ($payload['user_id'] ?? 0));

if ( ! $user ) {
return new \WP_Error('user_not_found', __('User not found.', 'ultimate-multisite'));
}

return [
'user_id' => $user->ID,
];
}

/**
* Generate a time-limited SSO token for cookie-less authentication.
* Check if a URL points to a different host from the main site.
*
* @since 2.0.11
*
* @param int $user_id User ID.
* @return string The token.
* @param string $url URL to check.
* @return bool
*/
private function generate_sso_token(int $user_id): string {
// Token expires in 5 minutes
$expiry = time() + 300;
$payload = wp_json_encode([
'user_id' => $user_id,
'exp' => $expiry,
]);
// HMAC-signed token
$hmac = hash_hmac('sha256', $payload, wp_salt('auth'));
private function is_cross_domain_url(string $url): bool {
$host = strtolower((string) wp_parse_url($url, PHP_URL_HOST));
$main_host = strtolower((string) wp_parse_url(get_site_url(), PHP_URL_HOST));
$scheme = strtolower((string) wp_parse_url($url, PHP_URL_SCHEME));

return base64_encode($hmac . '::' . $payload);
return ! empty($host) && ! empty($main_host) && $host !== $main_host && in_array($scheme, ['http', 'https'], true);
}

/**
Expand All @@ -647,40 +783,19 @@ public function handle_already_logged_in_on_login_page(): void {

// Check if this is an SSO flow (sso param or return_url param present)
$sso_action = $this->input('sso', '');
$return_url = $this->input('return_url', '');

// Also extract return_url from redirect_to if present
if ( empty($return_url) ) {
$redirect_to = $this->input('redirect_to', '');
if ( $redirect_to ) {
$parsed = wp_parse_url($redirect_to, PHP_URL_QUERY);
if ( $parsed ) {
parse_str($parsed, $query_params);
if ( ! empty($query_params['return_url']) ) {
$return_url = $query_params['return_url'];
}
}
}
}
$return_url = $this->get_sso_return_url();

// Check for SSO flow - either sso param or return_url pointing to different domain
if ( empty($sso_action) && empty($return_url) ) {
return;
}

// Get the subsite URL
$return_host = wp_parse_url($return_url, PHP_URL_HOST);
$main_host = wp_parse_url(get_site_url(), PHP_URL_HOST);

// Only redirect if actually going to a different domain
if ( ! $return_host || $return_host === $main_host ) {
if ( ! $this->is_cross_domain_url($return_url) ) {
return;
}

// Generate token and redirect to subsite
$token = $this->generate_sso_token(get_current_user_id());

$redirect_url = add_query_arg('wu_sso_token', $token, $return_url);
// Generate token and redirect to subsite.
$redirect_url = $this->add_cookie_less_sso_token($return_url, get_current_user_id());

wp_safe_redirect($redirect_url, 302, 'WP-Ultimo-SSO');
exit;
Expand All @@ -697,7 +812,7 @@ public function handle_already_logged_in_on_login_page(): void {
public function modify_login_form_defaults($defaults): array {

// Check if this is part of an SSO flow.
$return_url = $this->input('return_url', '');
$return_url = $this->get_sso_return_url();

if ( ! empty($return_url) ) {
// Set redirect_to to the subsite URL.
Expand Down
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