Basho\Riak\Node\Config::setCertificatePassword PHP Method

    public function setCertificatePassword($certificate_password)
    {
        $this->certificate_password = $certificate_password;
    }

 /**
  * usingCertificateAuthentication
  *
  * Build nodes with certificate authentication
  *
  * User authentication and access rules are only available in Riak versions 2 and above. To use this feature, TSL
  * is required to communicate with your Riak nodes.
  *
  * CURRENTLY NOT SUPPORTED OVER THE RIAK HTTP API
  *
  * @param $certificate
  * @param string $password
  *
  * @return $this
  * @throws Builder\Exception
  */
 public function usingCertificateAuthentication($certificate, $password = '')
 {
     $this->config->setCertificate($certificate);
     $this->config->setCertificatePassword($password);
     $this->config->setAuth(true);
     throw new Node\Builder\Exception('Riak over HTTP does not support Certificate Authentication.');
     return $this;
 }