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Implementing Authentication with Databases in Python

Authentication is the process of verifying the identity of a user. In many applications, this is done by checking a username and password against a database. In Python, you can implement this using libraries like sqlite3, mysql.connector, or SQLAlchemy along with password hashing tools like bcrypt.

Step-by-Step Guide (Using SQLite and bcrypt)

✅ 1. Set up the environment

You’ll need:

Python installed

sqlite3 (built-in with Python)

bcrypt (for password hashing)

Install bcrypt:

bash

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pip install bcrypt

✅ 2. Create a user table

python

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import sqlite3

# Connect to database (or create it)

conn = sqlite3.connect("users.db")

cursor = conn.cursor()

# Create users table

cursor.execute("""

CREATE TABLE IF NOT EXISTS users (

    id INTEGER PRIMARY KEY AUTOINCREMENT,

    username TEXT UNIQUE NOT NULL,

    password TEXT NOT NULL

)

""")

conn.commit()

conn.close()

✅ 3. Register (Sign Up) a New User

python

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import sqlite3

import bcrypt

def register_user(username, password):

    hashed_pw = bcrypt.hashpw(password.encode('utf-8'), bcrypt.gensalt())

    conn = sqlite3.connect("users.db")

    cursor = conn.cursor()

    try:

        cursor.execute("INSERT INTO users (username, password) VALUES (?, ?)", (username, hashed_pw))

        conn.commit()

        print("User registered successfully.")

    except sqlite3.IntegrityError:

        print("Username already exists.")

    finally:

        conn.close()

# Example usage

register_user("alice", "mypassword123")

✅ 4. Login (Authenticate) a User

python

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def login_user(username, password):

    conn = sqlite3.connect("users.db")

    cursor = conn.cursor()

    cursor.execute("SELECT password FROM users WHERE username = ?", (username,))

    result = cursor.fetchone()

    if result:

        stored_hashed_pw = result[0]

        if bcrypt.checkpw(password.encode('utf-8'), stored_hashed_pw):

            print("Login successful!")

        else:

            print("Incorrect password.")

    else:

        print("Username not found.")

    

    conn.close()

# Example usage

login_user("alice", "mypassword123")

Key Security Practices

Never store passwords in plain text. Always hash them using a secure algorithm like bcrypt.

Use parameterized queries (?) to prevent SQL injection.

Secure your database from unauthorized access.

Next Steps (Advanced)

Use a web framework like Flask or Django to build a web interface.

Implement sessions or JWT for logged-in users.

Add features like password reset, email verification, and login attempts limit.

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