form_fields.py

from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, SubmitField
from wtforms.validators import InputRequired, Length, EqualTo, ValidationError
from models import User
from passlib.hash import pbkdf2_sha256


class RegistrationForm(FlaskForm):
    """ Registration Form """

    username = StringField('username_label',
        validators=[
            InputRequired(message="Username required"),
            Length(min=4, max=25, message="Username must be between 4 and 25 characters")
        ]
    )
    password = PasswordField('password_label', 
        validators=[
            InputRequired(message="Password required"),
            Length(min=4, max=25, message="Username must be between 4 and 25 characters")
        ]
    )
    confirm_pswd = PasswordField('confirm_pswd_label',
        validators=[
            InputRequired(message="Password required"),
            EqualTo('password', message="Passwords must match")
        ])
    submit_button = SubmitField('Create')


    def validate_username(self, username):
        user_object = User.query.filter_by(username=username.data).first()
        if user_object:
            raise ValidationError('Username is incorrect')


# Even if we add params here, we don't need to pass the values explicitly, Flask wtforms automatically sends the data (form and field)
def invalid_credentials(form, field):
    """Username and password checker"""
    username_entered = form.username.data
    password_entered = field.data

    # check whether the data is valid or not 
    user_object = User.query.filter_by(username=username_entered).first()
    if user_object is None:
        raise ValidationError('Username or password is incorrect')
    elif not pbkdf2_sha256.verify(password_entered, user_object.password):
        raise ValidationError('Username or password is incorrect')

class LoginForm(FlaskForm):
    """ Login Form """

    username = StringField('username_label',
        validators=[
            InputRequired(message="Username required"),
        ]
    )
    password = PasswordField('password_label', 
        validators=[
            InputRequired(message="Password required"),
            invalid_credentials
        ]
    )
    submit_button = SubmitField('Submit')