flask log in system

from flask import Flask, render_template, url_for, request, session, redirect
from flask_pymongo import PyMongo
import bcrypt

app = Flask(__name__)

app.config['MONGO_DBNAME'] = 'flaskapp'
app.config['MONGO_URI'] = 'yourdburlhere'

mongo = PyMongo(app)

@app.route('/')
def index():
    return render_template('index.html')

@app.route('/register', methods=['POST', 'GET'])
def register():
    if request.method == 'POST':
        users = mongo.db.users
        existing_user = users.find_one({'name' : request.form['username']})

        if not existing_user:
            hashpass = bcrypt.hashpw(request.form['pass'].encode('utf-8'), bcrypt.gensalt()) 
            users.insert({'name' : request.form['username'], 'password' : hashpass})
            session['username'] = request.form['username']
            session['logged_in'] = True
            return redirect(url_for('index'))

        return 'That user is already taken'

    return render_template('register.html')

@app.route('/login', methods=['POST'])
def login():
    users = mongo.db.users
    login_user = users.find_one({'name': request.form['username']})

    if login_user:
        if bcrypt.hashpw(request.form['pass'].encode('utf-8'), login_user['password'].encode('utf-8')) == login_user['password'].encode('utf-8'):
            session['username'] = request.form['username']
            session['logged_in'] = True
            return redirect(url_for('index'))

        return 'Invalid username/password'

    return 'Invalid username'

@app.route('/logout')
def logout():
    session.clear()
    session['logged_in'] = False
    return render_template('index.html')

if __name__ == '__main__':
    app.secret_key = 'helloworld'
    app.run(debug=True)