Almost every program that we run has access to the environment, so nothing stops them from curling our credentials to some nefarious server.
Why don't we put credentials in files and then pass them to the programs that need them? Maybe coupled with some mechanism that prevents executables from reading any random file except those approved.
Basically just have each sets of credentials in a script, and whenever you need to use something that needs a key, you source the script you need first.