Exercise 2: What sslmode=require Is Missing — Possible Solution
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WHAT'S MISSING: sslmode=require only guarantees the connection is
ENCRYPTED — it does not verify that the server the client actually
connected to is the real, legitimate database server. The client will
accept ANY certificate presented to it, including a self-signed one or
one belonging to a completely different server, and proceed with an
"encrypted" connection regardless.

WHY THIS MATTERS: an attacker positioned to intercept the connection
(a man-in-the-middle) can present their OWN certificate instead of the
real database's, and sslmode=require will accept it without
complaint. The client ends up with a perfectly encrypted connection —
to the attacker, not to the real database — defeating the entire
purpose of using TLS in the first place while still giving a false
sense of security ("we have SSL enabled").

THE FIX: sslmode=verify-full. This setting does everything require
does (encrypts the channel) AND additionally verifies that the
server's certificate is signed by a trusted certificate authority AND
that the certificate's hostname actually matches the server being
connected to — the same two checks https1-5's chain-of-trust material
covers for HTTPS generally. (sslmode=verify-ca is a middle ground —
checks the CA signature but not the hostname match — verify-full is
the setting that closes the gap completely.)