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Flask Simple Login - Login Extension for Flask

Project description

Travis PyPI PyPI versions PyPI formats Flask

Login Extension for Flask

The simplest way to add login to flask!

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So why Flask Simple Login?

Sometimes you need something simple for that small project or for prototyping.

Flask Simple Login

What it provides:

  • Login and Logout forms and pages
  • Function to check if user is logged-in
  • Decorator for views
  • Easy and customizable login_checker
  • Basic-Auth for API endpoints

What it does not provide:

  • Database Integration
  • Password management
  • API authentication with Token or JWT
  • Role or user based access control

of course you can easily implement all above by your own. Take a look at example.

How it works

First install it from PyPI.

pip install flask_simplelogin

from flask import Flask
from flask_simplelogin import SimpleLogin

app = Flask(__name__)

That's it!

Now you have /login and /logout routes in your application.

The username defaults to admin and the password defaults to secret (yeah that's not clever, let's see how to change it)

Login Screen


Simple way

from flask import Flask
from flask_simplelogin import SimpleLogin

app = Flask(__name__)
app.config['SECRET_KEY'] = 'something-secret'
app.config['SIMPLELOGIN_USERNAME'] = 'chuck'
app.config['SIMPLELOGIN_PASSWORD'] = 'norris'


That works, but is not so clever, lets use env vars.


then SimpleLogin will read those env vars automatically.

from flask import Flask
from flask_simplelogin import SimpleLogin

app = Flask(__name__)
app.config['SECRET_KEY'] = 'something-secret'

But what if you have more users and more complex auth logic? write a custom login checker

Using a custom login checker

from flask import Flask
from flask_simplelogin import SimpleLogin

app = Flask(__name__)
app.config['SECRET_KEY'] = 'something-secret'

def only_chuck_norris_can_login(user):
    """:param user: dict {'username': 'foo', 'password': 'bar'}"""
    if user.get('username') == 'chuck' and user.get('password') == 'norris':
       return True  # <--- Allowed
    return False  # <--- Denied

SimpleLogin(app, login_checker=only_chuck_norris_can_login)

Using a custom login, logout or home URL

SimpleLogin automatically loads Flask configurations prefixed with SIMPLELOGIN_, thus to set a custom login, logout or home URL:

from flask import Flask
from flask_simplelogin import SimpleLogin

app = Flask(__name__)
app.config['SECRET_KEY'] = 'something-secret'
app.config['SIMPLELOGIN_LOGIN_URL'] = '/signin/'
app.config['SIMPLELOGIN_LOGOUT_URL'] = '/exit/'
app.config['SIMPLELOGIN_HOME_URL'] = '/en/'


Encrypt passwords

You can use the from import check_password_hash, generate_password_hash utilities to encrypt passwords.

A working example is available in of example app

Checking if user is logged in

from flask_simplelogin import is_logged_in

if is_logged_in():
    # do things if anyone is logged in

if is_logged_in('admin'):
    # do things only if admin is logged in

Protecting your views

from flask_simplelogin import login_required

@login_required  # < --- simple decorator
def foo():
    return 'secret'

@login_required(username='mary')  # < --- accepts a list of names
def bar():
    return "Mary's secret"

@app.route('/api', methods=['POST'])
@login_required(basic=True)  # < --- Basic HTTP Auth for API
def api():
    # curl -XPOST localhost:5000/api -H "Authorization: Basic Y2h1Y2s6bm9ycmlz" -H "Content-Type: application/json"
    # Basic-Auth takes base64 encripted username:password
    return jsonify(data='You are logged in with basic auth')

class ProtectedView(MethodView):  # < --- Class Based Views
    decorators = [login_required]
    def get(self):
        return "only loged in users can see this"

Protecting Flask Admin views

from import ModelView
from flask_simplelogin import is_logged_in

class AdminView(ModelView)
    def is_accessible(self):
        return is_logged_in('admin')

Customizing templates

There are only one template to customize and it is called login.html

Example is:

{% extends 'base.html' %}
{% block title %}Login{% endblock %}
{% block messages %}
   {%if form.errors %}
     <ul class="alert alert-danger">
       {% for field, errors in form.errors.items() %}
         <li>{{field}} {% for error in errors %}{{ error }}{% endfor %}</li>
       {% endfor %}
   {% endif %}
{% endblock %}

{% block page_body %}
       <form action="{{ url_for('simplelogin.login', next=request.args.get('next', '/')) }}" method="post">
            <div class="form-group">
            {{ form.csrf_token }}
            {{form.username.label}}<div class="form-control">{{ form.username }}</div><br>
            {{form.password.label}}<div class="form-control"> {{ form.password }}</div><br>
           <input type="submit" value="Send">
{% endblock %}

Take a look at the example app.

And you can customize it in anyway you want and need, it receives a form in context and it is a WTF form the submit should be done to request.path which is the same /login view.

You can also use {% if is_logged_in() %} in your template if needed.

Customizing or translating message alerts

The default message alerts are:

key message
login_success login success!
login_failure invalid credentials
is_logged_in already logged in
logout Logged out!
login_required You need to login first
access_denied Access Denied
auth_error Authentication Error: {0}

NOTE: the {0} in auth_error is a required placeholder to pass in the validator error message.

And you can customize by passing a dictionary:

app = Flask(__name__)
messages = {
    'login_success': 'Você está dentro!',
    'login_failure': 'ungültige Anmeldeinformationen',
    'is_logged_in': 'Iam initium',
    'logout': 'Déconnecté!',
    'login_required': 'Devi prima accedere',
    'access_denied': 'Acceso denegado',
    'auth_error': '授權錯誤: {0}'
SimpleLogin(app, messages=messages)

Custom validators

Pass must argument to login_required decorator, it can be a function or a list of functions if function returns None means No error and validator passed. if function returns an "Error message" means validator did not passed.

def be_admin(username):
    """Validator to check if user has admin role"""
    user_data = my_users.get(username)
    if not user_data or 'admin' not in user_data.get('roles', []):
        return "User does not have admin role"

def have_approval(username):
    """Validator: all users approved so return None"""

@login_required(must=[be_admin, have_approval])
def protected():
    return render_template('secret.html')

Take a look at the example app.


  • Flask-WTF and WTForms
  • SECRET_KEY set in your app.config


Do you need Access Control? you can easily mix flask_simplelogin with flask_allows pip install flask_allows

from flask import Flask, g
from flask_simplelogin import SimpleLogin
from flask_allows import Allows

app = Flask(__name__)
app.config['SECRET_KEY'] = 'something-secret'

def is_staff(ident, request):
    return ident.permlevel == 'staff'

def only_chuck_norris_can_login(user):
    if user.get('username') == 'chuck' and user.get('password') == 'norris':
       # Bind the logged in user data to the `g` global object
       g.user.username = user['username']
       g.user.permlevel = 'staff'  # set user permission level
       return True  # Allowed
    return False  # Denied

# init allows
allows = Allows(identity_loader=lambda: g.user)

# init SimpleLogin
SimpleLogin(app, login_checker=only_chuck_norris_can_login)

# a view which requires a logged in user to be member of the staff group
def a_view():
    return "staff only can see this"

Need JSON Web Token (JWT)?

Take a look at Flask-JWT-Simple and of course you can mix SimpleLogin + JWT Simple


Those extensions are really complete and production ready!

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