Hey @greggoryaddison
Just adding some more info here that relates more to the Unreal Engine. We use one of the .ini files in your Config folder to store the ID/Secret. Currently we use the DefaultEngine.ini but imagine you could use any/create your own. We then access that value in code using a 'UCLASS(config = Engine, defaultconfig)' class, with UPROPERTY(Config, EditAnywhere) for the ID/Secret.
During the build process, make sure you have 'bEncryptIniFiles' enabled in your DefaultGame.ini, we also have the value enabled in our DefaultCrypto.ini file too. There will also be an EncryptionKey value in the DefaultCrypto.ini file. When UE4 builds your packaged game, it will then use that encrytion key to obfuscate your .ini files - so even if someone had access to the package and the Unreal Engine - they would only get to the point were they would need that EncrytionKey to go any further.