I can't seem to get it to work. I suspect the problem is that Metabase requires me to set a password, but given the user authenticates using a key, there is no password.
Setting private_key_file=/data/Dev/metabase_test.key (note that using Windows style slashes produces a misleading error) seems to cause the driver to load the key; if I specify a non-existent file, it complains it can't load a key. However, when I try to connect, it says:
JWT token is invalid.
From experience, this is Snowflake-speak for "password incorrect." My theory is that given both password and private key, the Snowflake driver is choosing password.