Our build process currently makes use of separate keychains for signing different versions of our apps, specifically handling the signing of AppStore versus Enterprise variants. All of the keychain management is handled in our Fastlane scripts.
From what I can tell, it doesn’t looks like Bitrise has any support for keychains, only uploading certificates. I think it would be very helpful to allow uploading full named keychains so that we wouldn’t require a completely separate build process for Bitrise compared to what we would be running locally or on our current build servers.