The session key retrieved with get_session_key() is unusable, because of a bug in the function application/helpers/remotecontrol/remotecontrol_handle.php::_checkSessionKey which fails to read session data.
The bug results in all subsequent API requests being authenticated as Guest.

The problem is reading the value of $oResult->data ($oResult is of type Session), which in PostgreSQL instalation maps to a column of type bytea. The Yii framework maps this type to a stream instead of a string.

The following patch fixes the problem for me:

--- rch.php 2014-02-03 22:02:22.000000000 +0100
+++ application/helpers/remotecontrol/remotecontrol_handle.php 2014-02-03 22:01:47.000000000 +0100
@@ -2440,7 +2440,8 @@
return false;
else
{

• $this->_jumpStartSession($oResult->data);
• $data = fread($oResult->data, 1000);
• $this->_jumpStartSession($data);
  return true;
  }
  }