This applies to linux based systems only
Setting the environment variable SSL_CERT_DIR allows you to add some additional certificates to the (go) system cert pool, e.g. self-signed CAs for internal systems.
Note this is in addition to any root CAs that are already in your system level CA certificates files/bundles (see src/crypto/x509/root_linux.go;l=8-15
Side effect: setting this variable will cause the system to stop scanning the default cert directories https://cs.opensource.google/go/go/+/refs/tags/go1.16.7:src/crypto/x509/root_linux.go;l=17-23.
To mitigate this, you can use colon syntax to make sure all locations you want are scanned.
SSL_CERT_DIR=/etc/ssl/certs:/usr/local/ssl/my-custom-certs/