Requests a list of supported key attributes from the server.
Call this method to get a list of public key attributes supported by the server. This method is asynchronous and returns execution to the program at once it was called. After the request was processed, the OnAttribute event is fired 0 or more times passing attribute names to user. After all the attributes are passed the OnStatus event is fired which fired. Supported attributes request is possible only for protocol version 2 or higher.