This is a bit of a complicated process. You require a Google account but it should be free to create a service account.
There are 5 steps here: https://docs.dhis2.org/en/topics/tutorials/google-earth-engine-sign-up.html - do not skip any. The first four require you to use your Google account to create a service account and then create and download a JSON private key. It’s not made entirely clear from the DHIS 2 documentation, but you also need to register the service account to use Earth Engine - see the appropriate section of https://developers.google.com/earth-engine/guides/service_account.
You should change the name of the private key to dhis-google-auth.json.
The last step requires you to log into the server/VM running DHIS 2, upload the private key you got the from the initial steps (using e.g. scp or FileZilla) and change its permissions (see below for code for moving the file to the right location and ensuring the right permissions for the file). There is more detail on step 5 here: https://docs.dhis2.org/en/manage/performing-system-administration/dhis-core-version-239/installation.html#install_google_service_account_configuration
sudo mv dhis-google-auth.json /home/dhis/config/
sudo chown dhis:dhis /home/dhis/config/dhis-google-auth.jsonYou need to restart DHIS 2 (or reboot the VM/server) for DHIS 2 to reload its configuration. After that the Google Earth data sources (precipitation etc) should be accessible in the Maps app.