Version 1.3.4 introduced the change that when using TLS with `require_certificate` set to false, the client is no longer asked for a client certificate. This seemed to be causing problems in some situations, particularly with embedded devices. If `use_identity_as_username` is set to true when `require_certificate` is set to false, then the client will not be asked for a certificate, even if it has one configured. This means that the client will be refused access with connack code 4, "bad username or password", because if `use_identity_as_username` currently requires that a certificate is present, even if `allow_anonymous` is set to true. This change may cause unexpected results, but does not represent a security flaw because the change results in more clients being rejected than would otherwise have been.