authentication.php

<?php include 'db.php'; ?>
<?php
if ( !isset($_POST['email'], $_POST['password']) ) {
	// Could not get the data that should have been sent.
	exit('Please fill both the email and password fields!');
}
if ($stmt = $conn->prepare('SELECT id, password FROM users WHERE email = ?')) {
	// Bind parameters (s = string, i = int, b = blob, etc), in our case the username is a string so we use "s"
	$stmt->bind_param('s', $_POST['email']);
	$stmt->execute();
	// Store the result so we can check if the account exists in the database.
	$stmt->store_result();
}

if ($stmt->num_rows > 0) {
	$stmt->bind_result($id, $password);
	$stmt->fetch();
	// Account exists, now we verify the password.
	// Note: remember to use password_hash in your registration file to store the hashed passwords.
	if (password_verify($_POST['password'], $password)) {
		// Verification success! User has logged-in!
		// Create sessions, so we know the user is logged in, they basically act like cookies but remember the data on the server.
		session_regenerate_id();
		$_SESSION['loggedin'] = TRUE;
		$_SESSION['name'] = $_POST['email'];
		$_SESSION['id'] = $id;
		header("Location: dashboard.php?success=Login%20Success");
	} else {
		// Incorrect password
		echo 'Incorrect email and/or password!';
	}
} else {
	// Incorrect username
	echo 'Incorrect email and/or password!';
}
$stmt->close();
?>