$ curl -v https://yum.mariadb.org/RPM-GPG-KEY-MariaDB

* About to connect() to yum.mariadb.org port 443 (#0)

*   Trying 192.99.47.208... connected

* Connected to yum.mariadb.org (192.99.47.208) port 443 (#0)

* Initializing NSS with certpath: sql:/etc/pki/nssdb

*   CAfile: /etc/pki/tls/certs/ca-bundle.crt

  CApath: none

* Remote Certificate has expired.

* NSS error -8181

* Closing connection #0

* Peer certificate cannot be authenticated with known CA certificates

curl: (60) Peer certificate cannot be authenticated with known CA certificates

More details here: http://curl.haxx.se/docs/sslcerts.html

curl performs SSL certificate verification by default, using a "bundle"

 of Certificate Authority (CA) public keys (CA certs). If the default

 bundle file isn't adequate, you can specify an alternate file

 using the --cacert option.

If this HTTPS server uses a certificate signed by a CA represented in

 the bundle, the certificate verification probably failed due to a

 problem with the certificate (it might be expired, or the name might

 not match the domain name in the URL).

If you'd like to turn off curl's verification of the certificate, use

 the -k (or --insecure) option.