What are the key PHP functions or commands that can be used to validate user credentials against a database in a web application?

When validating user credentials against a database in a web application, key PHP functions or commands to use include mysqli_connect() to establish a connection to the database, mysqli_query() to execute a query to check if the user credentials are valid, mysqli_fetch_assoc() to retrieve the results of the query, and password_verify() to compare the hashed password stored in the database with the password entered by the user. 

<?php

// Establish a connection to the database
$conn = mysqli_connect("localhost", "username", "password", "dbname");

// Check if the connection was successful
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}

// Query to check if the user credentials are valid
$query = "SELECT * FROM users WHERE username = '$username'";
$result = mysqli_query($conn, $query);

// Retrieve the results of the query
$user = mysqli_fetch_assoc($result);

// Compare the hashed password stored in the database with the password entered by the user
if ($user && password_verify($password, $user['password'])) {
    // User credentials are valid
    echo "Login successful!";
} else {
    // User credentials are invalid
    echo "Invalid username or password";
}

// Close the database connection
mysqli_close($conn);

?>

Keywords

PHP database validation user credentials web application

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