> Which method should I use to secure it?
This opens up a whole area of digital security. I'd recommend looking for a course covering the basics, because if you don't know what you're doing, you'll probably make something so insecure a passer-by can at least delete everything, or possibly steal all the data - and if you are storing people's personal data, you can become liable for significant fines if that gets leaked and you were negligent in your security measures.
At a minimum look in to using HTTPS and protecting against injection attacks, but there's a lot more to it than that!
True but I'm thinking about security between mobile and server..
Any method requires data from device to validate the autentication.
My concern is more about if this data could be intercepted.
Does HTTPS encript all this information?
If yes, its fine for me..
About injection and everything, yeah, I know.. back when Mu servers were popular I had to learn about it. Never trust the client input