tracking tag. pageviews and duration on third party sites. API

I am looking for an API based application. No front end! I need a javascript tag which can be put on customers websites (Similar the Google Analytics). I will provide each tag with a unique ID. The tag will then store the ID, the URL and the duration the user was on that page. The application (Build in rails 4.* will then offer an API. I should be able to SECURELY consume this API from an application that I am building. The API should do the following: (for security, I presume a login, and login parameter to be made also.) getOverview(id, daterange[]) #daterange is optional #This will return a list of every page, a total pageview count and average time on page (Within a daterange, if daterange is provided) getSingle(id, url, daterange[]) #daterange is optional #this will return a single page, with how many views and average time on page (Within a daterange, if daterange is provided) I'd be happy to discuss any areas which are unclear. I believe this to be fairly straight forward. I DO NOT REQUIRE ANY VIEW FOR THIS APPLICATION. JUST AN API