import random


def get_authentication_code(code_length):
    """Generate a authentication code with appointed length.

    Args:
        code_length (int): The length of the authentication code.

    Returns:
        str: authentication code.
    """
    code_source = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'
    salt = ''
    for _ in range(code_length):
        salt += random.choice(code_source)
    return salt