Database Alternative to database.sparkfun.com which doesn't need a Private Key to Push Data

I have a project I am working on which will be open source. The project records data from all over. People can look at the instructions on a website, build the prototype, and the prototype will contribute its data to a giant database.

data.sparkfun.com/ is perfect for this, except for a major problem. In order to push data, you need to put the Private Key in the code (docs). This will also allow anybody with the code (which will be everybody looking at my project because it is open source) to edit, modify, and delete data from the database because they have the Private Key.

Is there any alternative to data.sparkfun for free so that I can achieve this? I am using NodeJS as the main language for my project.

EDIT: I also do not have a server to host my own database on. I also would need a hosting service (which is why data.sparkfun is so close to what I need).