As we've tried to tell you, SOAP doesn't work like this. Each request to a SOAP service point is independent of any that have gone before it. You can't 'Log On' as you put it. Each request must carry the authentication info, and the SOAP server will reject it or honour it as the security model sees fit.
You could have a SOAP method which returns user information, but that wouldn't imply any kind of 'session' being begun.
Tim
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"Your morbid fear of losing,
destroys the lives you're using." - Ozzy