Mark error in form using Bootstrap

Question

I\'ve started using Bootstrap in order to achieve a nice page design without resorting to GWT (the backend is made in java)

For my login screen I copied this example

Answer 1

For Bootstrap v4 use:
has-danger for form-group wrapper,
form-control-danger for input to show icon (will display ✖ at the end of input),
form-control-feedback to message wrapper

Example:

  
  
Not valid :(