如何自定义flask用户注册和登录功能？

from flask import Flask, render_template, request, redirect, url_for, session
from werkzeug.security import generate_password_hash, check_password_hash

app = Flask(__name__)
app.config['SECRET_KEY'] = 'your_secret_key'

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(100), unique=True, nullable=False)
    password = db.Column(db.String(100), nullable=False)

    def set_password(self, password):
        self.password = generate_password_hash(password)

    def check_password(self, password):
        return check_password_hash(self.password, password)

@app.route('/register', methods=['GET', 'POST'])
def register():
    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']

        user = User.query.filter_by(username=username).first()
        if user:
            return 'Username already exists'

        new_user = User(username=username)
        new_user.set_password(password)
        db.session.add(new_user)
        db.session.commit()

        return redirect(url_for('login'))

    return render_template('register.html')


@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 not user or not user.check_password(password):
            return 'Invalid username or password'

        session['user_id'] = user.id
        return redirect(url_for('home'))

    return render_template('login.html')

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