public function signature ( $request, $base_string, $consumer_secret, $token_secret )
	{
		// Fetch the private key cert based on the request
		$cert = $this->fetch_private_cert($request);
		
		// Pull the private key ID from the certificate
		$privatekeyid = openssl_get_privatekey($cert);
		
		// Sign using the key
		$sig = false;
		$ok  = openssl_sign($base_string, $sig, $privatekeyid);   
		
		// Release the key resource
		openssl_free_key($privatekeyid);
		  
		return $request->urlencode(base64_encode($sig));
	}