Return a JSON string explicitly from Asp.net WEBAPI?

In Some cases I have NewtonSoft JSON.NET and in my controller I just return the Jobject from my controller and all is good.

But I have a case where I get some raw JSON from another service and need to return it from my webAPI. In this context I can't use NewtonSOft, but if I could then I'd create a JOBJECT from the string (which seems like unneeded processing overhead) and return that and all would be well with the world.

However, I want to return this simply, but if I return the string, then the client receives a JSON wrapper with my context as an encoded string.

How can I explicitly return a JSON from my WebAPI controller method?

There are a few alternatives. The simplest one is to have your method return a HttpResponseMessage, and create that response with a StringContent based on your string, something similar to the code below:

public HttpResponseMessage Get()
{
    string yourJson = GetJsonFromSomewhere();
    var response = this.Request.CreateResponse(HttpStatusCode.OK);
    response.Content = new StringContent(yourJson, Encoding.UTF8, "application/json");
    return response;
}

And checking null or empty JSON string

public HttpResponseMessage Get()
{
    string yourJson = GetJsonFromSomewhere();
    if (!string.IsNullOrEmpty(yourJson))
    {
        var response = this.Request.CreateResponse(HttpStatusCode.OK);
        response.Content = new StringContent(yourJson, Encoding.UTF8, "application/json");
        return response;
    }
    throw new HttpResponseException(HttpStatusCode.NotFound);
}

Here is @carlosfigueira's solution adapted to use the IHttpActionResult Interface that was introduced with WebApi2:

public IHttpActionResult Get()
{
    string yourJson = GetJsonFromSomewhere();
    if (string.IsNullOrEmpty(yourJson)){
        return NotFound();
    }
    var response = this.Request.CreateResponse(HttpStatusCode.OK);
    response.Content = new StringContent(yourJson, Encoding.UTF8, "application/json");
    return ResponseMessage(response);
}