Almost Everything You Ever Wanted to Know About Web Authentication in Python

Everything You Ever Wanted to Know About Web Authentication in
Python @rdegges *Almost

I’m Randall Degges Run Developer Advocacy at Okta Python /
Node / Go Hacker

The Journey

REGISTER LOGIN DASHBOARD

0x00 - Getting Set Up

Assumptions Python https://www.python.org Mongo https://www.mongodb.com/

Install Dependencies $ pip install flask

Prepare the App $ touch server.py $ mkdir templates $
touch templates/base.html $ touch templates/index.html $ touch templates/register.html $ touch templates/login.html $ touch templates/dashboard.html

Create Basic Templates ➔ Home ➔ Register ➔ Login ➔
Dashboard

<html> <head> <title>Flask Simple Auth: {{ title }}</title> </head> <body>
{% block body %}{% endblock %} </body> </html> ➔ templates/base.html Home | Login | Register More HTML

{% extends "base.html" %} {% set title = 'Home' %}
{% block body %} <h1>Flask Simple Auth!</h1> <p> Welcome to Flask Simple Auth! Please <a href="/login">login</a> or <a href="/register">register</a> to continue. </p> {% endblock %} ➔ templates/index.html Use the base template Set the title variable Insert HTML into the body

{% extends "base.html" %} {% set title = 'Register' %}
{% block body %} <h1>Create an Account</h1> <form method="post"> <span>First Name:</span> <input type="text" name="firstName" required=true> <br> <span>Last Name:</span> <input type="text" name="lastName" required=true> <br> <span>Email:</span> <input type="email" name="email" required=true> <br> <span>Password:</span> <input type="password" name="password" required=true> <br> <input type="submit"> </form> {% endblock %} ➔ templates/register.html

{% extends "base.html" %} {% set title = 'Login' %}
{% block body %} <h1>Log Into Your Account</h1> <form method="post"> <span>Email:</span> <input type="email" name="email" required=true> <br> <span>Password:</span> <input type="password" name="password" required=true> <br> <input type="submit"> </form> {% endblock %} ➔ templates/login.html

{% extends "base.html" %} {% set title = 'Dashboard' %}
{% block body %} <h1>Dashboard</h1> <p>Welcome to your dashboard! You are now logged in.</p> {% endblock %} ➔ templates/dashboard.html

Create Basic Web App ➔ Define Views ➔ Render Templates
➔ Start Server

from flask import Flask from flask import render_template app =
Flask(__name__) @app.route("/") def index(): return render_template('index.html') @app.route("/login") def login(): return render_template('login.html') @app.route("/register") def register(): return render_template('register.html') @app.route("/logout") def logout(): pass @app.route("/dashboard") def dashboard(): return render_template('dashboard.html') ➔ server.py

@app.route("/") def index(): return render_template('index.html') Run the function below when
the user hits the / url Return a response to the user

$ FLASK_APP=server.py flask run Create Basic Templates

0x01 - Forms

<form method="post"> First Name: <input type="text" name="firstName" required> Last Name:
<input type="text" name="lastName" required> Email: <input type="email" name="email" required> Password: <input type="password" name="password" required> <input type="submit"> </form> You know... HTML!

from flask import jsonify from flask import request # ...
@app.route("/register", methods=['GET', 'POST']) def register(): if request.method == 'POST': return jsonify(request.form) return render_template('register.html') Form Data Tell the function to run for GET and POST requests

0x02 - Databases

$ mongo MongoDB shell version: 3.2.11 > Mongo

> use test; switched to db test The Basics >
show collections; > Get or create a database > db.users.insert({ email: "[email protected]", password: "woot!" }); WriteResult({ "nInserted" : 1 }) Show tables > db.users.find(); { "_id" : ObjectId("59247d0f3dacfc7ef19a41d2"), "email" : "[email protected]", "password" : "woot!" } Create table and insert something SELECT * FROM users;

$ pip install flask-pymongo app = Flask(__name__) app.config['MONGO_DBNAME'] = 'flask-simple-auth'
mongo = PyMongo(app) flask-pymongo

from flask import redirect from flask import url_for # ...
@app.route("/register", methods=['GET', 'POST']) def register(): if request.method == 'POST': mongo.db.users.insert_one(request.form.to_dict()) return redirect(url_for('dashboard')) return render_template('register.html') Creating Users Redirect to “/dashboard”

> db.users.find() { "_id" : ObjectId("59248139c6670c68737612bd"), "firstName" : "Randall", "lastName"
: "Degges", "email" : "[email protected]", "password" : "woot!", "__v" : 0 } Verifying

@app.route("/login", methods=['GET', 'POST']) def login(): if request.method == 'POST': user
= mongo.db.users.find_one({'email': request.form['email']}) if user['password'] == request.form['password']: return redirect(url_for('dashboard')) return render_template('login.html') Authenticating Users Find the user by email Verify the user’s password

0x03 - Sessions

Home Page Dashboard What If... Billing You had to enter
your credentials over and over again on every page you visited?

Website The Idea Login Unique ID Hey! Browser! Remember this
value! I need you to send it back to me next time you visit so I know who you are! Browser These are sessions.

Browser Server Cookies Cookies Authentication Cookies

HTTP Requests / Responses { "User-Agent": "Mozilla/5.0 ...", "Content-Type": "text/html"
} <html> … </html> Headers Body

Set-Cookie: session=12345 Body { "Set-Cookie": "session=12345" } Creating Cookies Set-Cookie:
a=b; c=d; e=f

Body { "User-Agent": "cURL/1.2.3", "Accept": "*/*", "Host": "localhost:3000", "Cookie": "session=12345"
} Reading Cookies

Using Sessions from flask import session # ... app.config['SECRET_KEY'] =
'SUPER_SECRET!' # ... @app.route("/login", methods=['GET', 'POST']) def login(): if request.method == 'POST': user = mongo.db.users.find_one({'email': request.form['email']}) if user['password'] == request.form['password']: session['id'] = str(user['_id']) return redirect(url_for('dashboard')) return render_template('login.html')

Verifying

from bson.objectid import ObjectId # ... @app.route("/dashboard") def dashboard(): if
'id' not in session: return redirect(url_for('login')) user = mongo.db.users.find_one({'_id': ObjectId(session['id'])}) if user: return render_template('dashboard.html') return redirect(url_for('login')) Improving the Dashboard If there’s no session, bail Find the user by id Everything OK? Show the dashboard

0x04 - Storing Passwords

{ "_id" : ObjectId("59248139c6670c68737612bd"), "firstName" : "Randall", "lastName" : "Degges",
"email" : "[email protected]", "password" : "woot!", "__v" : 0 } Current User Data

Password Hashing! Given a hash, you can never retrieve the
original password that created it. Hashes are one-way. The same password always generates the same hash.

Hashing • md5 • sha256 • bcrypt • scrypt •
argon2 • etc. • SHITTY • NOPE! • SAFE • AWESOME • YES!! • NO

bcrypt (pseudo) >>> password = 'hi' >>> hash = bcrypt(password)
>>> print(hash) '$2a$10$uS.pE0aS0NlsgbvLd6EruO5VDKllinIZLF3C84OYzWHFiyKYfZVXy'

Improving Registration $ pip install bcrypt passlib from passlib.hash import
bcrypt # ... @app.route("/register", methods=['GET', 'POST']) def register(): if request.method == 'POST': user_data = request.form.to_dict() user_data['password'] = bcrypt.hash(user_data['password']) user = mongo.db.users.insert_one(user_data) session['id'] = str(user['_id']) return redirect(url_for('dashboard')) return render_template('register.html')

Improving Login @app.route("/login", methods=['GET', 'POST']) def login(): if request.method ==
'POST': user = mongo.db.users.find_one({'email': request.form['email']}) if user and bcrypt.verify(request.form['password'], user['password']): session['id'] = str(user['_id']) return redirect(url_for('dashboard')) return render_template('login.html')

Our Improved User { "_id" : ObjectId("5924ad584f7ddf1eea467408"), "firstName" : "Randall",
"lastName" : "Degges", "email" : "[email protected]", "password" : "$2a$14$czZ5IJCRsi7TvqwW8InVsOOnzBffT3e19unr1ecFq0XQGiTatN0wm", "__v" : 0 }

Homework! http://plaintextoffenders.com/

0x05 - Refactoring

from flask import g from werkzeug.local import LocalProxy user =
LocalProxy(lambda: g.user) # ... @app.before_request def load_user(): if 'id' in session: g.user = mongo.db.users.find_one({'_id': ObjectId(session['id'])}) del g.user['password'] return Smart User Loading

from functools import wraps def login_required(func): @wraps(func) def decorator(*args, **kwargs):
if not user: return redirect(url_for('login')) return func(*args, **kwargs) return decorator Force Authentication GTFO Welcome buddy!

@app.route("/dashboard") @login_required def dashboard(): print('hello: {}'.format(user.first_name)) return render_template('dashboard.html') Refactoring

0x06 - CSRF

Let’s Say...  <form> <input type="text" name="amount"> <input
type="text" name="toAccount"> </form>

Cross Site Request Forgery Hey Randall, Check out this picture
of my dog! <img src="http://bank.com/withdraw?amount=1000000& toAccount=BadGuy">

CSRF Tokens Browser Server CSRF Cookie GET /login Login Page
w/ CT POST /login w/ CT NO! >:S

CSRF Protection in HTML <form method="post"> ... <input type="hidden" name="_csrf_token"
value="{{ csrf_token() }}"> </form>

CSRF Protection $ pip install flask-seasurf from flask_seasurf import SeaSurf
csrf = SeaSurf(app)

0x07 - Security Best Practices

User Server secret Always Use SSL

Use Cookie Flags from datetime import timedelta # Don't let
Javascript access cookies app.config['SESSION_COOKIE_HTTPONLY'] = True # Only set the cookie over SSL app.config['SESSION_COOKIE_SECURE'] = True # How long should the session last? app.config['PERMANENT_SESSION_LIFETIME'] = timedelta(minutes=30)

Don’t Roll Your Own ➔ Flask-Login ➔ Flask-Security ➔ Okta

Code https://github.com/rdegges Slides https://speakerdeck.com/rdegges Resources @oktadev @rdegges

BONUS! JWTs suck for web authentication.

What are JWTs? - JSON data - Cryptographically signed -
Not fancy - Not encrypted

What’s a Cryptographic Signature? Randall Degges That’s a signature!

What Do JWTs Actually Do? Prove that some data was
generated by someone else.

How Do People Use JWTs?

NOTE Never store sensitive information in LocalStorage / SessionStorage. NEVER
EVER.

“… In other words, any authentication your application requires can
be bypassed by a user with local privileges to the machine on which the data is stored. Therefore, it's recommended not to store any sensitive information in local storage.” - OWASP (Open Web Application Security Project)

Why Do JWTs Suck?

You’re Going to Hit the DB Anyway

Don’t Sign Things Twice Randall Degges That’s dumb! Randall Degges

What ARE JWTs Good For? Website Reset my password. Ok!
I’ve emailed you a link that has a JWT in the URL which will expire in 30 minutes. Ok! I clicked the link. This JWT looks legit. I suppose I’ll let you reset your password. Ok, your PW has been reset.

In Summary JWTs are not meant to be used for
persisting state. Making them do the same thing as cookies in a less efficient and secure manner is bad for you. Don’t use them unless you know how.

Almost Everything You Ever Wanted to Know About...

Almost Everything You Ever Wanted to Know About Web Authentication in Python

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