Bootstrap-vue and form validation

I recently learned about bootstrap-vue and find it very convenient. Being relatively new to vuejs I am trying to create a simple login form with validation and can’t for the life of me get it to work with the examples provided for a form containing more than one input field. My main obstacle stems from the fact that I want the form in a modal where the modal OK button needs to submit the form and only close the modal if form submission is successful. I simply adapted this form and put it in a modal, but can’t figure out how to trigger form submission/validation when NOT clicking the form submit button. What am I missing? Can someone provide a working example for form validation?