Steam API is not public, and only available to games/applications that were accepted by Steam.
In theory, I believe the API is applicable, but a public plugin in C2 is not to be expected anyway.
If you make a game that gets accepted/access to Steam, it's likely that Ashley could be of help and have access to some Steam "support" to include the API in your game.
Steam inclusion isn't the hardest part. Make a game that gets enough attention to access the platform and you won't be alone anyway to handle the API inclusion.