/**
* Generate a signed hash of the base string using the consumer and token
* as the signing key.
*
* $sig = $signature->sign($request, $consumer, $token);
*
* [!!] This method implements [OAuth 1.0 Spec 9.2.1](http://oauth.net/core/1.0/#rfc.section.9.2.1).
*
* @param Request request
* @param Consumer consumer
* @param Token token
* @return string
* @uses Signature::key
* @uses Request::base_string
*/
public function sign(Request $request, Consumer $consumer, Token $token = null)
{
// Get the signing key
$key = $this->key($consumer, $token);
// Get the base string for the signature
$base_string = $request->baseString();
// Sign the base string using the key
return base64_encode(hash_hmac('sha1', $base_string, $key, true));
}
