The ConnString type has functions to validate auth/ssl/etc, but this validation would not be done if ClientOptions were used instead of a URI. I wrote up a minimal example at https://gist.github.com/divjotarora/e4f8c9f14bfc154c857f9a1fb5a73f99. The clientFromURI function sees an error from NewClient because SCRAM-SHA-1 requires a username. The clientFromOpts function sees no error.