What are the key steps involved in decrypting an authentication string using the Rijndael AES algorithm in PHP?

To decrypt an authentication string using the Rijndael AES algorithm in PHP, you need to use the `openssl_decrypt` function with the appropriate parameters such as the encryption key, initialization vector (IV), and the cipher method. Make sure the key and IV used for decryption match the ones used for encryption to successfully decrypt the authentication string.

function decryptAuthenticationString($encryptedString, $key, $iv) {
    $decryptedString = openssl_decrypt(base64_decode($encryptedString), 'aes-256-cbc', $key, OPENSSL_RAW_DATA, $iv);
    return $decryptedString;
}

// Usage example
$encryptedString = "encrypted_authentication_string_here";
$key = "your_secret_key_here";
$iv = "your_iv_here";

$decryptedString = decryptAuthenticationString($encryptedString, $key, $iv);
echo $decryptedString;