Expired certificate

Ah, that looks like the CA root cert store on your RHEL7 is badly out of date.

That said, your cert is not necessarily bad. See a site like this and I think you will find it verifies successfully. Just enter your domain name and port 443 to test HTTPS access.

Do you need the WGET on your own server to succeed? Or are you just concerned by the message?

You are showing a part of the "long chain" that your server uses. Here is more background info on the long and short chains. Note that most sites use the long chain like yours even this forum website