import secrets

SALT_CHARS = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'


def gen_salt(length: int) -> str:
    """Generate a random string of SALT_CHARS with specified ``length``."""
    if length <= 0:
        raise ValueError('Salt length must be at least 1.')

    return ''.join(secrets.choice(SALT_CHARS) for _ in range(length))