Decode a base64-encoded string using the "modern" Python interface.

def base64_b64decode(instr):
    '''
    Decode a base64-encoded string using the "modern" Python interface.
    '''
    decoded = base64.b64decode(salt.utils.stringutils.to_bytes(instr))
    try:
        return salt.utils.stringutils.to_unicode(
            decoded,
            encoding='utf8' if salt.utils.platform.is_windows() else None
        )
    except UnicodeDecodeError:
        return decoded