I think it’s all read-only access through, so you can only use it to import data not make new transactions.
That’s alright. Even read-only access is useful. I could write a script that pulls my current investments, prompts for the amount I’ll be investing in total, and prints out the buys (eg “buy 10 x VOO, 5 x VXF, 20 x VXUS”) that’ll keep the account balanced based on some percentages.
For DNS challenges, I personally prefer using acme-dns. It’s a separate DNS server that only serves ACME DNS challenges. I felt a bit uneasy using an access token for my actual DNS host since it grants full read/write access to every record. acme-dns reduces the attack surface.
Let’s Encrypt follows CNAMEs and supports IPv6-only DNS servers, so you could just run acme-dns on a spare IPv6 address (assuming your internet provider has a static IPv6 range, or you have a VPS with IPv6).