[NEW] Take username from client certificate

[zuiderkwast]

The problem/use-case that the feature addresses

Avoid managing user passwords for ACL when we already use TLS with mutual authentication.

When password rotation is required and also certificate rotation is required, it becomes complex to rotate both of them.

Description of the feature

The server can take the username from the client's certificate, the comman name (CN=username) field. It seems to be common practice.

When this field matches an existing user, the client gets authenticated as this user as if the AUTH command had been used.

Alternatives you've considered

Use AUTH or HELLO and manage passords and do password rotation for each user, in addition to TLS certificates rotations.

Additional information