TIP: Are you asking yourself how to specify credentials (username and password) in your web service
The following documents on My Oracle Support will help you with this requirement:
Note 477891.1: Using a Local Business Service To customize transport features for a Siebel Outbound Web Service
Note 541317.1: Web Service - WS-Security digital signing
Note 979139.1: Adding Custom SOAP Headers to Outbound Web Service Calls With SOAP Filter Services
Note 1324943.1: Sample Filter service script to customize SOAP Envelope