The answers are going to depend on the specific protocol the company's site uses for these kinds of requests. You probably need to ask someone in the company's IT department about this, or search their web site for information. Every site will be different.

It is unlikely that their protocol would involve sending your username and password in clear text. That would be a pretty bad security hole.

Qt has a complete set of classes for handling XML, if that is the way your company provides data when you send a query.