src/web/Request.php
public function getCsrfToken($regenerate = false)
    {
        if ($this->_csrfToken === null || $regenerate) {
            if ($regenerate || ($token = $this->loadCsrfToken()) === null) {
                $token = $this->generateCsrfToken();
            }
            // the mask doesn't need to be very random
            $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-.';
            $mask = substr(str_shuffle(str_repeat($chars, 5)), 0, static::CSRF_MASK_LENGTH);
            // The + sign may be decoded as blank space later, which will fail the validation
            $this->_csrfToken = str_replace('+', '.', base64_encode($mask . $this->xorTokens($token, $mask)));
        }

        return $this->_csrfToken;
    }
public function getCsrfToken($regenerate = false)
    {
        if ($this->_csrfToken === null || $regenerate) {
            if ($regenerate || ($token = $this->loadCsrfToken()) === null) {
                $token = $this->generateCsrfToken();
            }
            // the mask doesn't need to be very random
            $chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-.';
            $mask = substr(str_shuffle(str_repeat($chars, 5)), 0, static::CSRF_MASK_LENGTH);
            // The + sign may be decoded as blank space later, which will fail the validation
            $this->_csrfToken = str_replace('+', '.', base64_encode($mask . $this->xorTokens($token, $mask)));
        }

        return $this->_csrfToken;
    }
Returns the token used to perform CSRF validation.

This token is a masked version of [[rawCsrfToken]] to prevent [BREACH attacks](http://breachattack.com/).
This token may be passed along via a hidden field of an HTML form or an HTTP header value
to support CSRF validation.
@param boolean $regenerate whether to regenerate CSRF token. When this parameter is true, each time
this method is called, a new CSRF token will be generated and persisted (in session or cookie).
@return string the token used to perform CSRF validation.