Android App HTTP json and security

I have a Android app that is a bit coded but cant get my head around http json get/post so i need someone that can create these for me it is needed asap really. The app has 2 screens Login screen and Account screen, Login screen needs the http json to login from api file is account exists it shows "auth":1 bit if it don't it shows "auth":0, IF "auth":1 go to Account screen the account screen needs to show in list Username, Status, Expire Date, Max Connections and Is Trial. On Account screen it has a close button so shared username and password need to go to next screen which is IPTV core the activity is setup to open IPTV core just needs coding better . Also on Login screen will like the username and password to be remembered automatically so when app is closed and opened back up the login details are still there. The biggest thing im after is something created on my server end to grab the DDNS from a code like CO746 and if code exists grab DDNS to do the login and Account info if not DDNS error this is so the app cannot be used by another provider and can only be used by myself and i can add other DDNS with other codes the file on the server must not be accessible by anyone to see. I know this is a long description but i want my app secure so no one can use it.