There have been a number of discussions in the community on how to specify a broker's connection details in a uri.

The result of the community discussion is captured here - https://github.com/mqtt/mqtt.github.io/wiki/URI-Scheme

In summary, the following uri format is proposed:

mqtt://[username][:password]@host.domain[:port][?clientid=clientid]

The uri scheme could alternative be 'mqtts' to specify a secure TLS connection should be used.

Other connection-time options (clean session etc) could also be expressed as query parameters.

A path portion of the uri could be used to specify a specific topic.

This JIRA can be addressed by way of Committee Note, rather than as an addition to the spec itsef.