Getting sharepoint logged user credentials to pass the SAP web service

Hi Team,

I am new to the Sharepoint 2010 . Please help me below issue as it was very urgent.

I created proxy for SAP web service . after programmatically  i should need to provide the user name and password for getting the outout from SAP web service methods.

How to get sharepoint logged in user name and password for passing to SAP web service ?

It is very urgent .