I want to build my web services serving JSON data utilizing RESTful architecture.
But I want my own client apps only that can request from my web services.
Basically, my web services contain sensitive data that is not for public consumption, but I wanted to build it that way so I can build many different client apps that connects to my web service.
Would appreciate any ideas for this, thanks.
You just need a couple things in place to do this. First, the service client will need to authenticate against your service (over HTTPS) to make a request. Once the client is authenticated, you can return a private token which the client has to include with this token. As long as the token expires after a reasonable amount of time, and a secure algorithm is used to generate it, this should do what you want.
If you have more strict security requirements, you can follow Jakob's suggestion, or have the client start a VPN session prior to making requests.
The fact that it's RESTful or uses JSON isn't a relevant factor when it comes to securing a web service. Any web service would need to be secured in the same manner. There are a few things you should do: