I learned how from +Erik Erickson's tutorial below (I'm subscribing to your channel, Erik!), via +Alicia Brooks of GEG Houston.
1. Question type: Choose Text.
2. Click on Advanced settings.
3. Select Data Validation.
4. Select Regular expression 5. Matches 6. Your password.
7. Type in Custom error text of your choice (e.g., Try again)
8. Make question required.
9. Click on Done.
10. Click on Add item.
11. Select Page break.
Here's a PDF of these instructions for download.
Thanks again, +Erik Erickson. You rock!