Password field with a three-bar strength metre
A password field with three bars under it and a show/hide toggle. Type and the bars light up one at a time, red to orange to green, with the label beside them changing to match.
Scoring is naive on purpose: length only, one bar to four characters, two to nine, three beyond. Anything you would ship needs a real estimator, run on a value that never leaves the page. The demo is the feedback, not the scoring.