Requests Tokenisation (CSRF-protection)

AJAX requests will go through a single module, core/request, which will attach the tokens
A pool of tokens will be managed simultaneously on the backend and frontend, to allow for concurrent requests
Forms will still be protected by the old method: a token is rendered by PHP to a hidden input field, and validated when the submitted form is received on the server

Specifications

To call a protected endpoint, the client must provide a token
If no token is provided, the request will be logged as a possible CSRF attempt
The token will be sent in the HTTP header of a tokenised request, under the X-CSRF-Token key
Each tokens cannot be used more than once
Tokens are stored on a per-user-session basis
A token may not live longer than the session of the user to which it belongs

Furthermore, a REST endpoint for such requests is expected to match the following criteria:

contentType : application/json; charset=UTF-8
headers : contains X-CSRF-Token value when needed
the responseBody: { success : true, data : [the results]} { success : false, data : {Exception}, message : 'Something went wrong' }
returns 204 for empty content

Frontend

How are the different components of this system related?

frontend

core/request module

At its heart, it is a basic $.ajax() request to a given URL. But the logic also includes fetching and attaching a token, and a mechanism which can force requests to run sequentially if desired.

Params:

* @param {Object} options
* @param {String} options.url - the endpoint full url
* @param {String} [options.method = 'GET'] - the HTTP method
* @param {Object} [options.data] - additional parameters (if method is 'POST')
* @param {Object} [options.headers] - the HTTP headers
* @param {String} [options.contentType] - what kind of data we're sending - usually 'json'
* @param {String} [options.dataType] - what kind of data expected in response
* @param {Boolean} [options.noToken = false] - if true, disables the token requirement
* @param {Boolean} [options.background] - if true, the request should be done in the background, which in practice does not trigger the global handlers like ajaxStart or ajaxStop
* @param {Boolean} [options.sequential] - if true, the request must join a queue to be run sequentially
* @param {Number}  [options.timeout] - timeout in seconds for the AJAX request

It returns:

* @returns {Promise} resolves with response, or reject if something went wrong

Usage example:

request({
    url: '/',
    method: 'POST',
    data: { foo: 'bar' },
    noToken: false
})
.then(function(response) {
    if (response.data && response.data.something) {
        doSomething();
    }
})
.catch(function(err) {
    logger.error(err);
})

tokenHandler

The tokenHandler is the middle-man between the core/request module and the core/tokenStore. It is not normally accessed directly, except in special cases (e.g. unit tests).

Usage:

// Initialise:
var tokenHandler = tokenHandlerFactory();

// Set an initial token:
tokenHandler.setToken('mytoken').then(function() {
    // ready to be used
});

// Retrieve and use a token (outside of a request):
tokenHandler.getToken().then(function(token) {
    // use token...
});

tokenStore

The tokenStore is an interface for the core/store browser-based storage component. It has been decided to create the tokenStore using the memory store implementation, for maximum security. The alternative indexeddb implementation could also be used instead, for example if it is necessary for the tokens to be shared between multiple open tabs of TAO.

Token format

A token is pretty simple, it looks like this when in storage:

{
    "value": "c8cd47bab63e1a6c4a9a9017252b1166131e996f",
    "ts": "1554907980137"
}

The timestamp allows tokens to be expired when they exceed the lifetime of the PHP session (24 minutes by default). This value can also be configured when instantiating the tokenHandler. If all the tokens in the frontend tokenStore expire, the user will be prompted to reload the page (thus delivering a fresh batch of tokens).

Token delivery mechanism

The tokens in the backend pool are provided to the frontend via the call to /tao/ClientConfig/config which is made on each page load.

Backend

Token pool generation

During a request the \tao_actions_ClientConfig::config() method is called. In this method we generate a token pool using the TokenService. This pool gets picked up and stored by the frontend.

Token Model

The Token model is the basic definition of a token object. It's a serializable object that contains the token's value, and the token's creation timestamp (float) generated by microtime(true). This model can be used to generate a new token by calling

$token = new Token();

Alternatively data can be passed to the Token class to initialize a predefined token. This can be achieved by calling:

$existingToken = [
    Token::TOKEN_KEY => 'exampletoken',
    Token::TIMESTAMP_KEY => 1556111298.3326
];

$token = new Token($existingToken);

TokenService

In the token service we handle the generation of the token pool, additionally the service is used to validate, and revoke tokens.

Protecting a request

In order to protect a request, we add a call to the \tao_actions_CommonModule::validateCsrf() method. This method checks if the token header is sent with the request, and if the token that was provided in this header is valid.

Validation failure

If a protected request did not receive the token header, or if the provided token is not valid, a \common_exception_Unauthorized() exception is thrown. This exception should be caught, and an appropriate response should be shown to the user. Currently this is done using the following control structure:

try {
    $this->validateCsrf();
} catch (common_exception_Unauthorized $e) {
    $this->response = $this->getPsrResponse()->withStatus(403, __('Unable to process your request'));
    return;
}

Protecting a Form

Forms are protected by a hidden element that contains the CSRF token. This token is not generated as part of the normal generation process, but instead gets appended to the token pool if a protected form is requested.

Protecting a form can be done by providing the csrf_protection option, as per the example below:

$formFactory = new tao_actions_form_CspHeader(
    ['serviceLocator' => $this->getServiceLocator()],
    [FormContainer::CSRF_PROTECTION_OPTION => true]
);

By providing this option, a \oat\tao\helpers\form\elements\xhtml\CsrfToken element gets added to the form. This handles the validation of the posted CSRF token, meaning the form will be invalidated if the CSRF validation fails.

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