This is a required sub-feature of the Topic tree, not an issue with what is currently specified.

Should be discussed in F2F together with DefaultBrokerPublishedId and topic tree

Beware of the following (from http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html ) - i.e. for the default to be guaranteed to work, it should not exceed 23 encoded bytes, and must contain only decimal digits and lowercase and uppercase English letters.

QUOTED:

The Server MUST allow ClientIds which are between 1 and 23 UTF-8 encoded bytes in length, and that contain only the characters

"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ" [MQTT-3.1.3-5].

The Server MAY allow ClientId’s that contain more than 23 encoded bytes. The Server MAY allow ClientId’s that contain characters not included in the list given above.

Use Hash of ApplicationUri as default for ClientId
Can be used as default PublisherId / Topic Tree

7.3.5.4 Connection properties

If the ClientID is not configured, the PublisherId is used as ClientID. If the PublisherId is a UInteger, the value is converted to a String.

See also resolution of 0008754 for the content of the PublisherId

Agreed to changes in virtual F2F.