Hello,
You could save it in secrets and then get it in and out of your app with the necessary code for it.
Secrets are made available via env variables to the app.
There’s likely a size limit for any given secret, in the order of a few kilobyes or so.
At least that’s what I remember reading a few days ago.
Ref: How are you managing cert files with Fly?
You could put it into volumes as well.
Ref: Where to store CockroachCloud CA certificate? - #2 by jerome