Saves the token to your local keychain under a service called "ecmwfr".
wf_set_key(user, key, service)
user (email address) used to sign up for the ECMWF data service
token provided by ECMWF
which service to use, one of
It invisibly returns the user.
In systems without keychain management set the option keyring_backend to `file` (i.e. options(keyring_backend = "file")) in order to write the keychain entry to an encrypted file. This mostly pertains to headless Linux systems. The keychain files can be found in ~/.config/r-keyring.