def METHOD_NAME(self):
    cleaned_data = super().METHOD_NAME()
    password = cleaned_data.get("password")
    if password and self.user and self.user.has_usable_password():
        user_exist = authenticate(username=self.user.username, password=password)
        # Check if the user exist.
        if not user_exist and password != "":
            self._errors["password"] = self.error_class([_("Mot de passe incorrect.")])
            if "password" in cleaned_data:
                del cleaned_data["password"]
    return cleaned_data