Handle custom metadata to a user account

[Tilix4]

Hi, is there a way to write/read custom metadata to a user account?
The use case is for an application built over ATproto, I want to add features that doesn't exist in Bluesky, and because I want to allow authentication from bluesky accounts, the easiest way would be to store the data relevant to my features directly to the user account metadata, instead of storing them on my own DB.
Thank you very much for you awesome work!