How to Create a Login Form with Postgres and Python - Part 5: Update DB With New Password

Introduction

In this tutorial, we will build a registration system that allows users of your Postgres- and Python-based web application to create a username and password, add the new user to our database, send that new user a confirmation email, receive a response from their click on the link we sent them in that email, and set a flag in the PostgreSQL database that the user is confirmed. This article is part four of a five-part series. In this series, we will address the following: – Part 1: Build the sign-in form using HTML, CSS, and Javascript. Interaction with the database will be absent from this part 1. – Part 2: Validate user input of email and password, create a hash of the user’s password, and compare it to the hash we have in our PostgreSQL database. Using Python for this. If they verify, we send them on to the rest of the application. – Part 3: Email the user a link because they clicked the “I forgot my password” button. – Part 4: Serve the user a form to create a new password. – Part 5: Using Python and PostgreSQL, we handle the final updating of the database with their new password and then send them back to the login screen.

Overview of this article

In this part 5, we update the database with the new password the user gave us in the last form.

Assumptions and prerequisites

We’ll assume you have followed the instructions in parts 1, 2, 3, and 4, starting here: here.

The code

Final version of your Python code! Paste the code below into your favorite code editor, save the file as “_sign/in.py“, upload to your server, and try it out! IMPORTANT: When we say “study the code below,” this is important for more reasons than one. For example, you may need to install some new Python libraries.

from flask import Flask
from flask import render_template # to render the html form
from flask import request # to get user input from sign-in form
import hashlib # included in Python library, no need to install
import psycopg2 # for database connection
from flask_mail import Mail
from flask_mail import Message

app = Flask(__name__)

# Mail creds
def smtp_config(config_name, smtp=1):
    with open(config_name) as f:
            config_data = json.load(f)
    if smtp not in {1,2}:
        raise ValueError("smtp can only be 1 or 2")
    if smtp==2:
        MAIL_USERNAME = config_data['MAIL_USERNAME'][1]
        MAIL_PASSWORD = config_data['MAIL_PASSWORD'][1]
    else:
        MAIL_USERNAME = config_data['MAIL_USERNAME'][0]
        MAIL_PASSWORD = config_data['MAIL_PASSWORD'][0]
    MAIL_SERVER = config_data['MAIL_SERVER']
    MAIL_PORT = config_data['MAIL_PORT']
    MAIL_USE_TLS = bool(config_data['MAIL_USE_TLS'])
    return [MAIL_USERNAME, MAIL_PASSWORD, MAIL_SERVER, MAIL_PORT, MAIL_USE_TLS]
# Set up the mail object we will use later.
mail = Mail()

# Database creds
t_host = "database address"
t_port = "5432" #default postgres port
t_dbname = "database name"
t_user = "database user name"
t_pw = "database user password"
db_conn = psycopg2.connect(host=t_host, port=t_port, dbname=t_dbname, user=t_user, password=t_pw)
db_cursor = db_conn.cursor()

@app.route("/")

def showForm():
    # Show our html form to the user.
    t_message = "Login Application"
    return render_template("sign_in.html", message = t_message)

@app.route("/sign_in", methods=["POST","GET"])
def sign_in():
    t_stage = request.args.get("forgot")
    ID_user = request.args.get("ID_user")
    t_email = request.form.get("t_email", "")
    if t_stage == "login" OR t_stage == "reset":
        t_password = request.form.get("t_password", "")

    # Check for email field left empty
    if t_email == "":
        if t_stage == "forgot":
            t_message = "Reset Password: Please fill in your email address"
        else:
            t_message = "Login: Please fill in your email address"
        # If empty, send user back, along with a message
        return render_template("sign_in.html", message = t_message)

    # Check for password field left empty
    # Note we are checking the t_stage variable to see if they are signing in or they forgot their password
    #   If they forgot their password, we don't want their password here. We only want their email address
    #   so we can send them a link in the next part of this article.
    # In both 1st stage and 3rd, we harvest password, so t_stage is "login" or "reset"
    if (t_stage == "login" OR t_stage == "reset") AND t_password == "":
        t_message = "Login: Please fill in your password"
        # If empty, send user back, along with a message
        return render_template("sign_in.html", message = t_message)

    # In both 1st stage and 3rd, we harvest password, so t_stage is "login" or "reset"
    if t_stage == "login" OR t_stage == "reset":
        # Hash the password
        t_hashed = hashlib.sha256(t_password.encode())
        t_password = t_hashed.hexdigest()

    # Get user ID from PostgreSQL users table
    s = ""
    s += "SELECT ID FROM users"
    s += " WHERE"
    s += " ("
    s += " t_email ='" + t_email + "'"
    if t_stage != "login":
        s += " AND"
        s += " t_password = '" + t_password + "'"
    s += " AND"
    s += " b_enabled = true"
    s += " )"

    db_cursor.execute(s)

    # Here we catch and display any errors that occur
    #   while TRYing to commit the execute our SQL script.
    try:
        array_row = cur.fetchone()
    except psycopg2.Error as e:
        t_message = "Database error: " + e + "/n SQL: " + s
        return render_template("sign_in.html", message = t_message)

    # Cleanup our database connections
    db_cursor.close()
    db_conn.close()

    ID_user = array_row(0)

    # If they have used the link in the email we sent them then t_stage is "reset"
    if t_stage == "reset":
        # UPDATE the database with new password
        s = ""
        s += "UPDATE users SET"
        s += " t_password = '" & t_password & "'"
        s += "WHERE"
        s += "("
        s += " ID=" + ID_user
        s += ")"
        # IMPORTANT WARNING: this format allows for a user to try to insert
        #   potentially damaging code, commonly known as "SQL injection".
        #   In a later article we will show some methods for
        #   preventing this.

        # Here we are catching and displaying any errors that occur
        #   while TRYing to commit the execute our SQL script.
        db_cursor.execute(s)
        try:
            db_conn.commit()
        except psycopg2.Error as e:
            t_message = "Reset password: Database error: " + e + "/n SQL: " + s
            return render_template("sign_in.html", message = t_message)
        db_cursor.close()
        # They got this far, meaning they were found in the database

    # First stage. They have filled in username and password, so t_stage is "login"
    if t_stage == "login":
        # UPDATE the database with a logging of the date of the visit
        s = ""
        s += "UPDATE users SET"
        s += " d_visit_last = '" & now() & "'"
        s += "WHERE"
        s += "("
        s += " ID=" + ID_user
        s += ")"
        # IMPORTANT WARNING: this format allows for a user to try to insert
        #   potentially damaging code, commonly known as "SQL injection".
        #   In a later article we will show some methods for
        #   preventing this.

        # Here we are catching and displaying any errors that occur
        #   while TRYing to commit the execute our SQL script.
        db_cursor.execute(s)
        try:
            db_conn.commit()
        except psycopg2.Error as e:
            t_message = "Login: Database error: " + e + "/n SQL: " + s
            return render_template("sign_in.html", message = t_message)
        db_cursor.close()

        # Redirect user to the rest of your application
        return redirect("http://your-URL-here", code=302)

    # If they have clicked "Send me a password reset link" then t_stage is "forgot"
    if t_stage == "forgot":
        # Send email to the user
        smtp_data = smtp_config('config.json', smtp=1)
        app.config.update(dict(
        MAIL_SERVER = smtp_data[2],
        MAIL_PORT = smtp_data[3],
        MAIL_USE_TLS = smtp_data[4],
        MAIL_USERNAME = smtp_data[0],
        MAIL_PASSWORD = smtp_data[1],
        ))
        mail.init_app(app)
        # Set up smtp (send mail) configuration
        t_subject = "Password reset link"
        t_recipients = t_email
        t_sender = "server@yourapplication.poop"

        # Build message body here
        s = ""
        s += "Dear " + s_email + "<br>"
        s += "<br>"
        s += "Thank you for playing!" + "<br>"
        s += "<br>"
        s += "Here is your password reset link. Please click on the following link or paste it into your web browser:" + "<br>"
        s += "<br>"
        s += "<a href='http://YOUR APP DOMAIN NAME HERE/sign_in.py?forgot=step2&ID_user=" + ID_user
        s += "'>https://YOUR APP DOMAIN NAME HERE/sign_in.py?forgot=step2&ID_user=" + ID_user
        s += "</a>" + "<br>"
        s += "<br>"
        s += "If you have any questions, feel free to reply to this message." + "<br>"
        s += "<br>"
        # Set up our mail message
        msg = Message(
            body = s,
            subject = t_subject,
            recipients = [t_recipients],
            sender = t_sender,
            reply_to = t_sender
            )

        # Send the email
        mail.send(msg)

        # Show user they are done and remind them to check their email.
        t_message = "Login: Password reset link was sent to your email address."
        return render_template("sign_in.html", message = t_message)

    # If they have used the link in the email we sent them then t_stage is "reset"
    if t_stage == "reset":
        # Show user they are done and they need to log in using their new password.
        t_message = "Login: Your password has been reset."
        return render_template("sign_in.html", message = t_message)

# This is for command line testing
if __name__ == "__main__":
    app.run(debug=True)

Conclusion

Congratulations! You’ve now completed the tutorial on how to create a login for your Python / PostgreSQL application.

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