class User(models.Model):
    # mandatory
    username = models.CharField(max_length=129, unique=True, db_index=True)
    password = models.CharField(max_length=256)
    REQUIRED_FIELDS = ('password',)
    USERNAME_FIELD = 'username'

    # properties
    name = models.CharField(max_length=60, blank=True)
    email = models.CharField(max_length=254, blank=True)
    birth_date = models.DateField(null=True, blank=True)
    profile_image = s3_field(blank=True)
    profile_background_image = s3_field(blank=True)
    profile_message = models.CharField(max_length=100, blank=True)
    couple = models.ForeignKey(Couple, blank=True, null=True, db_index=True)

    # metadata
    created = created_field()
    last_login = models.DateTimeField(auto_now=True)
    is_active = models.BooleanField(default=True)
    is_staff = models.BooleanField(default=False)
    is_superuser = models.BooleanField(default=False)
    social = JSONField(blank=True, null=True)

    @staticmethod
    def _digest_password(password):
        us = settings.USER_SECRET
        algorithm_ = us['algorithm']
        hkey = us['hkey']
        iteration = us['iteration']
        return hexlify(pbkdf2_hmac(algorithm_, password.encode(), hkey, iteration)).decode()

    @staticmethod
    def create_user(username, password):
        User.objects.create(username=username, password=User._digest_password(password))