Please refer to the following page to find instructions on how to install and keep updated a local installation of IGTF CA certificates:
https://docs.egi.eu/providers/operations-manuals/howto01_using_igtf_ca_distribution/
IGTF_CA_CERT_PATH=/etc/grid-security/certificates/
IGTF_CA_CERT_BASE_URL=https://repository.egi.eu/sw/production/cas/1/current/tgz/
sudo mkdir -p ${IGTF_CA_CERT_PATH}
FILELIST="$(curl -s ${IGTF_CA_CERT_BASE_URL} | sed -n 's/^.*href="\(.*\.tar\.gz\)">.*$/\1/p')"
for file in ${FILELIST}; do
curl ${IGTF_CA_CERT_BASE_URL}/$file | sudo tar xz --strip-components=1 -C "${IGTF_CA_CERT_PATH}"
done