feat: add checkServerIdentity override

[brandonjfeldkamp]

This fixes the issue described by https://github.com/sidorares/node-mysql2/pull/2119#issuecomment-1655735558 and partially resolves https://github.com/sidorares/node-mysql2/issues/2172.

This doesn't implement the changes described in the issue regarding deprecating the Amazon RDS profile in favor of moving that out to a new package but it does allow for a path forward to re-enabling rejectUnauthorized.

The follow scenarios are now true:

• Set rejectUnauthorized: false - never any server identity verification

• Set rejectUnauthorized: true or not provided:

  • set verifyIdentity: true or not provided - run provided checkServerIdentity() or use default tls.checkServerIdentity() function

  • set verifyIdentity: false - checkServerIdentity set to no-op function

How was this tested?

I tested changes locally against a tls-enabled postgresql instance. I'm not sure of how to incorporate any unit or integration tests for this as there does not currently appear to be any. Any support here would be lovely.

[wellwelwel]

Just linking 🔗

• #2253

[brandonjfeldkamp]

while the code around this change in your active memory - could you also please help reviewing #2295 ? That would be a minor version bump as it adds checkServerIdentity option. I don't like the fact that we would have 2 similarly named flags ( one is flag, one is function with custom check logic ), but might still worth adding

@juanheyns @sidorares regarding this concern of similarly named "things" from #2376, would you like me to rename it? I think this is still important as without it by setting the verifyIdentity flag to false you become more vulnerable to MITM attacks. By overriding the checkServerIdentity function we could enforce server identity in a way that makes sense for us. This is my line of thinking at least, does it make sense?