Complex settings menu (dynamically updated from server-side)

Hi,

I would like to create a complex settings menu with 2 requirements:
1. Validate credentials on server side and notify the user of valid\invalid
2. If credentials are correct, I would like to fill a combo box (“values”) with server-side provided list that specific to this user.

For example, here is a flow for my settings:
1. the user enters the settings menu and see 3 different settings (username, password, and empty combo box selection)
2. the user enters the username\password
3. the add-on will let the user know if the credentials are correct
4. the add-on will fill the combo box with values (the third settings) based on the user’s data on the server
5. the user will select one of the options in the combo box.

I didn’t find anything remotely close to this. I saw that there is an “action” on the “setting” node but couldn’t find anything that will allow me to run Python code upon changes and fill a combo box data.

Thanks!
Lidan