Website User Tracking

Need a Javascript tag to be developed which should act as follows: 1. When loaded in a webpage, it should run a script to capture given data points (such as IP address or browser useragent). Now there are 2 lists of variables to be captured, first one being a list of 15 and second one being list of 40, each should be able to act independently. 2. This script should work such as the actual list of variables being collected cannot be determined via console or a tag manager. 3. This script should send data to our server as a JSON object. 4. The same user (with same cookie ID) needs to be identified across different sessions on the same browser. We need to have codes for doing this via both 1st and 3rd party cookies. If not using cookies, feel free to suggest alternative ways (such as local storage). Needs to work across both desktop and mobile browsers. 5. Each user will correspond to a profile in our backend. Hence the JSON payload sent to server must contain some kind of user identifier to match user behavioral events to given profile. 6. Logged in users need to be identified via UID and linked to the same user identifier as above. 7. A documentation needs to be prepared as well, to clearly understand the mechanism to add/remove variables in future, as well as the user matching tactics used. Feel free to ask any queries you may have. In many ways this is similar to how Google Analytics works. Thanks!