By pressing Enter inside the password field, submit the form?

By pressing Enter inside the password field, submit the form?

I'm trying to achieve that if the focus is on password-field (#edit-password), and the user press the Enter key on his keyboard, the form get submitted:


But in my above example it seems that it doesn't matter if the focus is on password field or on any other field, pressing the Enter key will always submit the form!

Why is that?