AB test tools for REST APIs

I've got a REST API used to power movie recommendations. We occasionally tweak the algorithm and want a subset of request to go to this new version. I'm familiar with a large number of website A/B tools like Optimizely, but they all seem to be target towards HTML content or integration into mobile apps.

I think my need is much simpler, but would prefer not building this myself.

Does anyone know any tools for ab testing and things like:

• Have two urls which return json (uses basic auth for credentials)
  1. http://ift.tt/1N1Y2XI
  2. http://ift.tt/1N1Y02c
• Want to have a single URL we can use to segement 10% of requests to go to URL #1, the rest go to URL #2