akkoma/docs/docs/configuration/howto_proxy.md

How to configure upstream proxy for federation

If you want to proxify all http requests (e.g. for TOR) that Akkoma makes to an upstream proxy server, edit your config file (dev.secret.exs or prod.secret.exs) and add the following:

config :pleroma, :http,
  proxy_url: "127.0.0.1:8123"

The other way to do it, for example, with Tor can be done like so:

config :pleroma, :http, proxy_url: {:socks5, :localhost, 9050}