Yep, that’s why I was asking whether it needs to be 2-way. If not you can use weak encryption such as MD5. But you say you have to use base64 regardless so that rules out the string filters.
Not aware of anything doable in Shopify Liquid. But hey, who knows - seen JSON parsers written in Liquid!!! ?
adding in here for reference just in case anyone else ends up here in this obscure corner of the shopify forum - you 100% can encode to base64 in liquid using base64_encode so the above accepted answer not correct.
working in order printer app and order emails for me.
apparently you can use | base64_decode for also but not tested.
only time I’ve been asked in like 10 years so not a common one.