login page in python flask with database

from flask import Flask, render_template, request, redirect, url_for
from flask_sqlalchemy import SQLAlchemy
from werkzeug.security import generate_password_hash, check_password_hash
from flask_login import UserMixin, login_user, LoginManager, login_required, current_user, logout_user

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///site.db'
app.config['SECRET_KEY'] = 'your_secret_key'
db = SQLAlchemy(app)
login_manager = LoginManager(app)

class User(UserMixin, db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(150), nullable=False, unique=True)
    password = db.Column(db.String(256), nullable=False)

@login_manager.user_loader
def load_user(user_id):
    return User.query.get(int(user_id))

@login_manager.unauthorized_handler
def unauthorized_callback():
    return redirect(url_for('login'))

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']
        user = User.query.filter_by(username=username).first()
        if user and check_password_hash(user.password, password):
            login_user(user)
            next_page = request.args.get('next')
            return redirect(next_page) if next_page else redirect(url_for('index'))
    return render_template('login.html')

@app.route('/logout')
@login_required
def logout():
    logout_user()
    return redirect(url_for('login'))