Revamp SSL documentation

[byte]

Make sure we talk about SSL for MariaDB Server and MySQL 8. There are config differences. also Percona XtraDB Cluster (PXC) 8 has SSL on by default

Address the below report:
We stumbled upon some problems today when we wanted to move Galera
Replication from standard to SSL:

[ERROR] WSREP: handshake with remote endpoint ssl://10.96.0.13:4567 failed: asio.ssl:337047686: 'error:1416F086:SSL routines:tls_process_server_certificate:certificate verify failed')

and also:

Looking for 'mysql' as: /usr/bin/mysql Version check failed. Got the following error when calling the 'mysql' command line client ERROR 2026 (HY000): SSL connection error: Validation of SSL server certificate failed

After we were reading through your documentation we found 2 topics which
would have saved us some time:

https://galeracluster.com/library/documentation/ssl-cert.html

1. It was not clear to the customer, that a Galera node also needs the
   client key and certificate (he thought that this is only necessary for
   client-server communication). So I suggest to you to make a red frame
   around this sentence as well:

"Each node requires both to secure client activity and state snapshot
transfers."

Possibly listening all files which are needed would help as well???

2. Further: Documentation statement:

"In the event that this verification fails, repeat the above process to
generate replacement certificates."

is not really helpful because if you do our mistake you will end up in
the same situation again and again. We found out, that above error
happens because of this:

https://stackoverflow.com/questions/19726138/openssl-error-18-at-0-depth-lookupself-signed-certificate

"Whatever method you use to generate the certificate and key files, the
Common Name value used for the server and client certificates/keys must
each differ from the Common Name value used for the CA certificate.
Otherwise, the certificate and key files will not work for servers
compiled using OpenSSL."

As soon as we used different CN (instead of Enter, Enter, Enter, ...) it
worked. So you could add a hint stating this?

[kirjaamo]

Would these sove this issue:

1. I make a note out of "Each node requires both to secure client activity and state snapshot transfers."
2. I add a sentence after "In the event that this verification fails...", stating that "The Common Name value used for the server and client certificates/keys must each differ from the Common Name value used for the CA certificate. Otherwise, the certificate and key files will not work for servers compiled using OpenSSL."

[byte]

This would move things further, but I think this is more a placeholder for me, to also do blogs/tutorials on this

[kirjaamo]

OK. I added those. There's a bracnh for you to continue.