ASMX store username and password on Web.config

Hi there, 

My Web Service is connecting to another web service  which needs authentication. 

This is NOT a windows authentication, so I have hard coded the username and password at the moment. 

This is obviously not a good practice. 

How do I store the username and password for a proprietary system please ?

What section should I add to Web.config and how do I retrieve the data. 

Kind regards, 

Peter