Encode a string as base64 using the "legacy" Python interface.

    Among other possible differences, the "legacy" encoder includes
    a newline ('\\n') character after every 76 characters and always
    at the end of the encoded string.

def base64_encodestring(instr):
    '''
    Encode a string as base64 using the "legacy" Python interface.

    Among other possible differences, the "legacy" encoder includes
    a newline ('\\n') character after every 76 characters and always
    at the end of the encoded string.
    '''
    return salt.utils.stringutils.to_unicode(
        base64.encodestring(salt.utils.stringutils.to_bytes(instr)),
        encoding='utf8' if salt.utils.platform.is_windows() else None
    )