The provided key is invalid sounds like a problem with a key file of yours. It isn't. The server's certificate was signed by a different CA that has the same name as the one in your SslCa file, and MySQL's automatic CAs all have the same name.
The certificate authority (CA) does not match means the check worked: the server's certificate wasn't signed by the CA in your SslCa file. But it caught me a second time when the right CA was in the file, because MySql.Data reads only the first certificate in it.
The key was good, and MySQL had made it itself, yet the driver said The specified file cannot be converted to a key. It isn't the key, it's the wrapping: MySql.Data reads only one of the two formats that OpenSSL writes, and it isn't the one you get today by default.
SslMode=VerifyCA worked. Moving up to VerifyFull, which only adds a check of the server's name, failed with a complaint about a client certificate I'd never needed. The driver insists on one with PEM files, and then it never sends it.
I raised SslMode from Required to VerifyCA and the connection stopped working, with No file path has been provided for the connection option SslCa. VerifyCA means "check who signed the server's certificate", so the driver needs to know which signature to trust, and it only looks in the file you give it.
No error page and no 500: the whole API process ended, in the middle of a burst of requests. The message mentions authentication and I/O, and neither was the problem. The real cause is more requests at once than Maximum Pool Size, and a callback inside the driver that throws where nothing can catch it.
tlsv1 alert protocol version is the server telling the client that it won't use that TLS version. The two have nothing in common, and the fix is to find what each allows.
SSL error: Unable to get private key in the MySQL image usually means MySQL can't read the key file, not that there's anything wrong with it. MySQL runs as user 999 in that image. And the server starts anyway, with no working TLS, which is easy to miss.
CA certificate ca.pem is self signed turns up in MySQL's log every time it starts, and I went looking for what I'd done wrong. Nothing. Every root CA is self-signed, by definition, so MySQL's own automatic CA triggers it on a default install.
Failed to validate certificate … because certificate has expired is a warning, not an error, so MySQL starts and accepts TLS connections as usual. Clients that check certificates will refuse it. Clients that don't won't notice, which is the worst of both.
