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[LTI] fix: LTI 1.3 launch fails when another request of the session runs in parallel #12383

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Merged
Saaweel merged 1 commit into from
Nov 5, 2026
+131 −23
Merged

[LTI] fix: LTI 1.3 launch fails when another request of the session runs in parallel #12383

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139 changes: 122 additions & 17 deletions components/ILIAS/LTIConsumer/classes/class.ilLTIConsumerContentGUI.php
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,26 @@ class ilLTIConsumerContentGUI
public const CMD_LAUNCH = 'launch';
public const CMD_SHOW_EMBEDDED = 'showEmbedded';

/**
* Query parameter that carries the authentication request of the tool from ltiauth.php to the launch,
* instead of the session: a parallel request of the same session writing the session back later would
* remove it again, e.g. the asynchronous requests of the main bar while an embedded launch is running.
*/
public const LTI13_LOGIN_PARAM = 'lti13_login';

private const LTI13_LOGIN_KEYS = [
'scope',
'response_type',
'client_id',
'redirect_uri',
'login_hint',
'lti_message_hint',
'state',
'response_mode',
'nonce',
'prompt'
];

protected ilObjLTIConsumer $object;

protected ilCmiXapiUser $cmixUser;
Expand Down Expand Up @@ -94,16 +114,17 @@ protected function launch(): void
$this->dic->toolbar()->addText($this->getStartButtonTxt11());
}
} else {
if ($this->object->isLaunchMethodEmbedded() && (ilSession::get('lti13_login_data') == null)) {
$loginData = $this->getLTI13LoginData();
if ($this->object->isLaunchMethodEmbedded() && $loginData === null) {
$tpl = new ilTemplate('tpl.lti_content.html', true, true, 'components/ILIAS/LTIConsumer');
$tpl->setVariable("EMBEDDED_IFRAME_SRC", $this->dic->ctrl()->getLinkTarget(
$this,
self::CMD_SHOW_EMBEDDED
));
$this->dic->ui()->mainTemplate()->setContent($tpl->get());
} else {
if (ilSession::get('lti13_login_data') != null) {
$form = $this->getLoginLTI13Form();
if ($loginData !== null) {
$form = $this->getLoginLTI13Form($loginData);
if ($form == null) {
// $this->dic->ui()->mainTemplate()->setOnScreenMessage('failure', 'initialLogin Error: ' . $err, true);
$this->dic->ui()->mainTemplate()->setOnScreenMessage('failure', 'initialLogin Error: ', true);
Expand All @@ -120,10 +141,11 @@ protected function launch(): void
}
}

protected function getLoginLTI13Form(): ?string
protected function getLoginLTI13Form(array $loginData): ?string
{
$loginData = ilSession::get('lti13_login_data');
ilSession::clear('lti13_login_data');
if (!$this->dic->access()->checkAccess('read', '', $this->object->getRefId())) {
return null;
}
$err = $this->validateLTI13InitalLogin($loginData);
if ($err !== null) {
return null;
Expand All @@ -134,7 +156,6 @@ protected function getLoginLTI13Form(): ?string
if (isset($loginData['state'])) {
$params['state'] = $loginData['state'];
}
ilSession::clear('lti_message_hint');
$r = '<form action="' . $loginData['redirect_uri'] . "\" name=\"ltiAuthForm\" id=\"ltiAuthForm\" " .
"method=\"post\" enctype=\"application/x-www-form-urlencoded\">\n";
if (!empty($params)) {
Expand Down Expand Up @@ -252,9 +273,8 @@ protected function getStartButtonTxt13(): string

$target = $this->object->getLaunchMethod() == "newWin" ? "_blank" : "_self";
$button = '<input class="btn btn-default ilPre" type="button" onClick="ltilaunch()" value = "' . $this->lng->txt("show_content") . '" />';
$ltiMessageHint = (string) $this->object->getRefId() . ":" . CLIENT_ID;
$ltiMessageHint = self::getLTI13MessageHint($this->object->getRefId());
$html = $this->dic->refinery()->encode()->htmlSpecialCharsAsEntities();
ilSession::set('lti_message_hint', $ltiMessageHint);
$output = '<form id="lti_launch_form" name="lti_launch_form" action="' . $html->transform($this->object->getProvider()->getInitiateLogin()) . '" method="post" target="' . $target . '" encType="application/x-www-form-urlencoded">';

$output .= sprintf('<input type="hidden" name="%s" value="%s" />', 'iss', $html->transform(ilObjLTIConsumer::getIliasHttpPath())) . "\n";
Expand Down Expand Up @@ -290,9 +310,8 @@ protected function getEmbeddedAutoStartFormular(): string

$target = "_self";
$output = '';
$ltiMessageHint = (string) $this->object->getRefId() . ":" . CLIENT_ID;
$ltiMessageHint = self::getLTI13MessageHint($this->object->getRefId());
$html = $this->dic->refinery()->encode()->htmlSpecialCharsAsEntities();
ilSession::set('lti_message_hint', $ltiMessageHint);
$output = '<form id="lti_launch_form" name="lti_launch_form" action="' . $html->transform($this->object->getProvider()->getInitiateLogin()) . '" method="post" target="' . $target . '" encType="application/x-www-form-urlencoded">';
$output .= sprintf('<input type="hidden" name="%s" value="%s" />', 'iss', $html->transform(ilObjLTIConsumer::getIliasHttpPath())) . "\n";
$output .= sprintf('<input type="hidden" name="%s" value="%s" />', 'target_link_uri', $html->transform($this->getTargetLinkUri())) . "\n";
Expand Down Expand Up @@ -460,7 +479,7 @@ private function validateLTI13InitalLogin(array $loginData): ?string

$ok = !empty($scope) && !empty($responsetype) && !empty($clientid) &&
!empty($redirecturi) && !empty($loginhint) &&
!empty($nonce) && (ilSession::get('lti_message_hint') != null);
!empty($nonce) && self::isValidLTI13MessageHint((string) $ltimessagehint, $this->object->getRefId());

if (!$ok) {
$error = 'invalid_request';
Expand All @@ -474,11 +493,6 @@ private function validateLTI13InitalLogin(array $loginData): ?string
$error = 'unsupported_response_type';
}
if ($ok) {
list($ref_id, $ilias_client_id) = explode(':', ilSession::get('lti_message_hint'), 2);
if ((int) $this->object->getRefId() !== (int) $ref_id) {
$ok = false;
$error = 'invalid_request';
}
if ($this->object->getProvider()->getClientId() !== $clientid) {
$ok = false;
$error = 'unauthorized_client';
Expand Down Expand Up @@ -535,6 +549,97 @@ private function validateLTI13InitalLogin(array $loginData): ?string
}
}

/**
* The lti_message_hint of a launch: the object and the ILIAS client, signed for the session and the user.
* The tool sends it back unchanged with its authentication request, so the launch can be checked without
* keeping anything in the session.
*/
public static function getLTI13MessageHint(int $ref_id): string
{
$hint = $ref_id . ':' . CLIENT_ID;

return $hint . '.' . self::signLTI13MessageHint($hint);
}

/**
* The lti_message_hint without its signature, as ltiauth.php reads the object and the ILIAS client from it.
*/
public static function getUnsignedLTI13MessageHint(string $hint): string
{
if (preg_match('/^(.+)\.[0-9a-f]{64}$/', $hint, $matches) === 1) {
return $matches[1];
}

return $hint;
}

private static function isValidLTI13MessageHint(string $hint, int $ref_id): bool
{
return session_id() !== '' && hash_equals(self::getLTI13MessageHint($ref_id), $hint);
}

private static function signLTI13MessageHint(string $hint): string
{
global $DIC;

return hash_hmac('sha256', $hint . '|' . $DIC->user()->getId(), (string) session_id());
}

/**
* The link ltiauth.php sends the browser to with the authentication request of the tool, which goes on
* with the launch of the object.
*/
public static function getLTI13LaunchLink(int $ref_id, string $ilias_client_id, array $data): string
{
global $DIC;

$login_data = [];
foreach (self::LTI13_LOGIN_KEYS as $key) {
if (isset($data[$key]) && is_string($data[$key])) {
$login_data[$key] = $data[$key];
}
}
$encoded = rtrim(strtr(base64_encode(json_encode($login_data, JSON_THROW_ON_ERROR)), '+/', '-_'), '=');

$ctrl = $DIC->ctrl();
$ctrl->setParameterByClass(ilObjLTIConsumerGUI::class, 'ref_id', $ref_id);
$ctrl->setParameterByClass(self::class, self::LTI13_LOGIN_PARAM, $encoded);
$ctrl->setParameterByClass(self::class, 'client_id', $ilias_client_id);

return $ctrl->getLinkTargetByClass(
[ilRepositoryGUI::class, ilObjLTIConsumerGUI::class, self::class],
self::CMD_LAUNCH,
'',
false,
false
);
}

/**
* The authentication request of the tool passed on by ltiauth.php, null when the request has none.
*/
private function getLTI13LoginData(): ?array
{
$value = $this->getRequestValue(self::LTI13_LOGIN_PARAM);
if (!is_string($value) || $value === '') {
return null;
}
$json = base64_decode(strtr($value, '-_', '+/'), true);
$data = is_string($json) ? json_decode($json, true) : null;
if (!is_array($data)) {
return null;
}

$login_data = array_fill_keys(self::LTI13_LOGIN_KEYS, null);
foreach (self::LTI13_LOGIN_KEYS as $key) {
if (isset($data[$key]) && is_string($data[$key])) {
$login_data[$key] = $data[$key];
}
}

return $login_data;
}

// TODO: request_wrapper?

/**
Expand Down
15 changes: 9 additions & 6 deletions components/ILIAS/LTIConsumer/resources/ltiauth.php
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Original file line number Diff line number Diff line change
Expand Up @@ -158,7 +158,7 @@ function sanitizeJson(string $string)

}

$parts = explode(":", $ltiMessageHint, 3);
$parts = explode(":", ilLTIConsumerContentGUI::getUnsignedLTI13MessageHint($ltiMessageHint), 3);
$isContentSelection = false;
$ref_id = '';
$il_client_id = '';
Expand Down Expand Up @@ -189,14 +189,17 @@ function sanitizeJson(string $string)
$DIC->http()->close();
}
$url = "../../../" . $redirect_target;
// only persist the login data once the request has fully passed validation,
// so a rejected request never leaves unvalidated data behind in the session
ilSession::set('lti13_login_data', $data);
} else {
$url = "../../../goto.php?target=lti_" . $ref_id . "&client_id=" . $il_client_id;
// the launch of an object gets the authentication request with the link, not in the session: a parallel
// request of the same session would remove it again when it writes the session back
$data['client_id'] = $clientId;
$url = ilObjLTIConsumer::getIliasHttpPath() . '/'
. ilLTIConsumerContentGUI::getLTI13LaunchLink((int) $ref_id, $il_client_id, $data);
}

// only persist the login data once the request has fully passed validation,
// so a rejected request never leaves unvalidated data behind in the session
ilSession::set('lti13_login_data', $data);

function buildSameSiteNoneSessionCookieHeader(): ?string
{
if (session_status() !== PHP_SESSION_ACTIVE || session_id() === '') {
Expand Down
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