I was trying to figure out which authentication mechanism that new users would use by default, and it looks like SCRAM-SHA-256 is the default for 4.4 and 5.0. I couldn't determine this value from the logs in 4.2.

I think it would be useful to include this in the logs, so that customers know if they are not specifying authMechanism in the URI string, their db users will use SHA-256:

https://www.mongodb.com/docs/manual/reference/connection-string/#mongodb-urioption-urioption.authMechanism

I'm not sure if it's important, but without specifying anything in the db.createUser command about the auth mechanism, the users all get created with SHA-1 and SHA-256 under the "mechanisms" field.