How do I provide internet access only to a single Android app?
Try Opera Max to restrict per app data access to mobile and Wi-Fi networks. The PlayStore description says it,


  
  Block apps &amp; prevent data leakage:
  Control your apps’ internet usage by blocking apps from running in the background that are using mobile data or Wi-Fi without
  permission.Blocking apps running in the background conserves battery and minimises your battery usage.
  


If you want to restrict only a particular app follow the steps,


Open Settings menu > Data Usage
Select the app you want to restrict the data.
And select "Restrict background data"


If you are on a Wi-Fi network and you want to restrict the app accessing data in the background using your wi-fi connection, do the above steps in the Wi-Fi Tab to restrict the app access to Wi-Fi network too.