I deliberated between re-using the json file in the android app and using a sqlite database or some such thing, given that a UI for editing these will have to be implemented at some point. I figure the json file is more config than data, and probably should be as consistent as possible between platforms.
For now at least this makes the app usable for me, without having to hard-code my server credentials.
note that blindly trusting the name/extension of the file has security ramifications if you don't know what you are doing (and even if the extension is correct, e.g. if you upload a php file to a php enabled server). It is expected you know what you are doing since you have full control of the server.