certificate to secure the connection to the client (signed by `proxy-ca.pem`).
If an error occurs in the validation (missing `certificate-*.pem` files,
-fingerprint changed, etc.) it's logged by the proxy (stdout) and the special
+fingerprint changed, etc.) it's logged by the proxy (stderr) and the special
`proxy-invalid.pem` certificate is used to send a 500 error message to the
client. The connection to the server is closed so there's no chance that any
client data is sent to the (possible) evil server. The invalid certificate is