To add a certificate (for example your or your organization's internal CA certificate) to the systemwide list of trusted certificates, place the new certificate in /usr/local/share/ca-certificates/.
mkdir -p /usr/local/share/ca-certificates/
cp path/to/my.crt /usr/local/share/ca-certificates/
Make sure users have necessary read access to the directory/certificates, or users won't trust them due to read failures. Also make sure untrusted users don't have write access!Then either run
emerge -1 app-misc/ca-certificates