libs-base/Resources/GSTLS

Files here are the fallbacks for TLS/SSL certificate verification.

To find the certificate authority certificates the system looks in:
The path specified by GSTLSCAFile (if that user default is defined),
otherwise the path specified in the GS_TLS_CA_FILE environment variable
if it is defined, otherwise the file GSTLS/ca-certificates.crt in the
base library resource bundle.

Similarly to find the revoke file, the order of precedence of configuration
is GSTLSRevokeFile, GS_TLS_REVOKE_FILE, GSTLS/revoke.crl

ca-certificates.crt
        a list of PEM encoded certificates of trusted authorities

        NB. This is just the list of trusted authorities from my personal
        machine, it may not be suitable for you ... please replace/remove
        to meet your own needs.

revoke.crl

        may be set to a revocation list for certificates which have been
        revoked by the trusted authorities.
        At present, no revocation list is provided.

You may want to put keys here too ...if you have an openssl 'traditional' style
key you may (depending on your version of gnutls: newer versions can read
openssl specific keys) need to convert it to the standard PKCS8 format.
You can use openssl to do that as follows:

openssl pkcs8 -topk8 -v2 des3 -in old_key.pem -out new_key.pem

You will be asked (3 times) for the password for the key, as the tool needs to
decrypt it and encrypt it again in standard format.