Require password for each application to install Since I will be lending my phone to someone else, I want my phone to ask my Google account password (or alternative authentication) each time an app is installed.

If I go to Google Play -> Three bars menu -> Settings -> Require authentication for purchases, the options are:


For all purchases through Google Play on this device.
Every 30 minutes.
Never.


The first option seems to be what I am looking for.
Nevertheless, I am not asked for any authentication for installing apps.

Can this be done? How?

Using a Samsung Galaxy J7, with Android 6.0.1.
Apps that are free don't have to be purchased -> no purchase means no password prompt. 

I see two possibilities for you:


Delete your Google account from the device. Google apps usually sync everything to the cloud, therefore by re-adding the account everything will be restored.
If the device has the possibility to create a guest user account set a difficult password on your primary account and create a guest user. Guest users aren't allowed to install new apps, however they can use every app that is already installed and the app data is stored in a separate directory therefore the guest can use the apps but don't access your app data.