Making a Flask app with login functionality

Hi there guys! In this post I will share my experience with you while developing a Flask app with login functionality. The sourcecode of the app is available here.

We will be using the following libraries:

Flask (obviously)
Flask-SQLAlchemy
Jinja2
SQLAlchemy
Werkzeug
Flask-WTF

First-of-all we will define a User model. It goes something like this:

class User(db.Model):
    __tablename__ = 'user'
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(120))
    password = db.Column(db.String(120))
    email = db.Column(db.String(240))

    def __init__(self, name, email, password):
        self.name = name
        self.email = email
        self.set_password(password)

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

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

    def __repr__(self):
        return '<User %r>' % self.name

We did a couple of things here. They are:

Assigned user as the tablename
created 4 fields with id as the primary_key
created 2 custom methods, set_password and check_password.
Modified the output of __repr___ to make it more user-friendly

The 2 custom methods allow us to save password hashes instead of plain-text passwords. Always make sure that you save only the hashes and not the plain-text passwords so that if you database is somehow compromized, the plain-text passwords are not leaked.

Views:

There are four views in my app. Namely:

home
login
signup
logout

###home:

This route simply redirects to the login view if the user is not logged in. We check that the user is logged in or not by running the following code:

if session['user_name']:

This only runs if there is a user_name key in the session dict. So if there is not user_name in the session dict we simply redirect the user to login by running this code:

return redirect(url_for('login'),401)

401 stands for un-authorized. This status code tells the user that he is not authorized to view this page.

###login:

In this view we create an instance of the LoginForm and present it to the user if he is not logged in. If the user submits the form correctly and a user with the email specified exists in our server, we redirect the user to the home view. We check that the user_email is in the database and the password is correct by running the following code:

user = User.query.filter_by(email=form.email.data).first()
if user is not None and user.check_password(form.password.data):

If it is correct then we modify the session variables by running this code:

session['user_email'] = form.email.data
session['user_name'] = user.name

If it is incorrect then we present the errors to the user and ask him/her to try again.

###signup:

This view is kind-of similar to the login view. In this view we create an instance of the SignupForm form and present it to the user. If the form is validated on submit then we create a user in our database with the supplied information.

Finally, we redirect the user to the home view.

###logout:

This view simply pops the user_name and user_email values from the session dict.

There is one other decorated method as well. It is check_user_status. It is called before every request. It allows us to modify a couple of variables to our liking. We use it to modify the session variable.

Conclusion:

The key here is the session dict. We use it to check whether the user is logged-in or not. I hope you enjoyed this short intro. You can always checkout the whole source-code of the app.py file from the project to get a better understanding.

yasoob/post.md

Making a Flask app with login functionality

Views:

Conclusion: