For AC GRDIFR download you must visite the link gridfr, click in "Obtenir le certificat de l'AC", and then import all CA files in your browser.
In the Browser ( ex: Firefox ), open the "Certificate Manager" search the MENESR authority and export to PEM files all entries.
For the case:
To trust a certificate authority you must:
Save your custom certificate authority file(s) to the directory
"/etc/pki/ca-trust/source/anchors"
And run
$ update-ca-trust enable
$ update-ca-trust
Save your custom certificate authority file(s) to the directory
"/usr/local/share/ca-certificates"
After that to update the trusted certificate authority file of the OS run
$ /usr/sbin/update-ca-certificates