Setting the Authentication type for WsdlRequest programmatically

I am not sure if you can possibly avoid that by following the below as that does not require all that.

Here is you go:
1. Go to Preferences, Http Settings, Authentication Preemtive and click the check box and save the preferences.

2. In the project, go the interface (typicaly wsdl that is being imported) and provide the credentials details. You may do the same for other interfaces in the project.

From now onwards, the security details are being sent automatically along with WsdlRequest.

See if this works for you.