Classes don’t uniquely identify particular fields. That’s what the ID attribute is for. That looks like the developer of the website needs to follow best practice and give it a unique ID.
I agree that classes are not the best for this purpose, however, as a last-resort thing, if no other option is found to identify the field, this could be a functional workaround.
It runs the risk of creating false positives, where your password or other credentials are filled into various unrelated fields on the webpage. To prevent this, there would also have to be an opt-in option “Match to Class”, which would be possible but create UI clutter.