Is there a way, using JavaScript only (client side), to ensure that an HTTP request is actually coming from my Phonegap application?  

Be aware: I'm not talking about authenticating *the user*, rather, in a sense, about authenticating *the app itself*. There isn't (and mustn't be) any kind of user interaction related to this.  

Not even talking about confidentiality of the communication (I'm not using HTTPS and the payload is not encrypted).
My guess is, in the end, this inevitably requires some sort of *hard-coded key*.  

The problem is, as you can see for example [here](https://stackoverflow.com/q/6160554/1836314), such a key would be usually accessible by almost anyone - and this problem comes up not only with Javascript assets, but also with Java in Android.
If no way with Phonegap or any Cordova plugin, could you suggest an equivalent framework (or environment like Icenium) that could make this thing possible?  

Or, at last, would there be any *real* risk in not taking this precaution for the aforesaid scenario?

EDIT: Kurt Du Bois reminded me I did not mention SSL client authentication. Be it applicable/convenient or not, it always ends up to the problem of keeping a private key secret. I find this is well described [here](https://security.stackexchange.com/a/14590), and summed up in the sentence: "the assurance that the key hasn't been exported is only as strong as the key store itself".