Add an enforced format to the expiration date

forms.py

@@ -56,7 +56,7 @@ class LoginForm(FlaskForm):
 
 
 class RegistrationCodeForm(FlaskForm):
-    expiration_time = DateField('Expiration Time', validators=[Optional()])
+    expiration_time = DateField('Expiration Time', format='%Y-%m-%d', validators=[Optional()])
     max_usages = IntegerField('Max Usages', validators=[NumberRange(min=1)])