I'd probably be tempted to set this up as two separate surveys. In the first, turn off all the browser data capture fields and have one question on the first page (same page as the "start" question) : a single-select with Yes and No. Set up the "Yes" option as an "Other Specify", and modify the text to ask for their "User Name". When they click "Next", the "No" response should skip to a terminate page marking them as disqualified, while the "Yes" shoud flow to a terminate page that redirects to the second survey, passing in their "Other-Specify" answer as their password. This second survey can capture their browser data and other information if desired.