Add support for JSON

[debbbbie]

No description provided.

[nicolasblanco]

Hey thanks for your PR !

Do you know if there may be security issues with the fact to accept JSON ?

[iMacTia]

I'm not entirely convinced about this.
If my request contains a JSON, then my whole request body should be of type JSON and Rails would parse that for me automatically (so that would be validated as an Hash).
Having a JSON structure in the params makes me feel like something strange or wrong is going on and that shouldn't really happen...

Do you have a real-world scenario of when this might happen?