Detailed steps to reproduce the problem?

opts.ApplyURI(...).SetAuth(options.Credential{AuthMechanism: "MONGODB-AWS"})

When I try to connect with these client options, I get the following error:

MONGODB-AWS source must be empty or $external 

However, AuthSource is empty here...I would expect it to be set to $external, which is what happens when the auth mechanism is specified in the URI instead of through the client options (source).

https://github.com/mongodb/specifications/blob/master/source/auth/auth.md#mongocredential-properties-5

Definition of done: what must be done to consider the task complete?

Using SetAuth with an AuthMechanism of MONGODB-AWS should not result in an error if AuthSource is unspecified.

I'm no Go Driver expert, but I think this is happening because of this line: https://github.com/mongodb/mongo-go-driver/blob/1649d33597960a4863fc4e8009e146576edcc61d/x/mongo/driver/topology/topology_options.go#L178

Could this be an issue in other drivers?

The exact Go version used, with patch level:

$ go version

1.22.2

The exact version of the Go driver used:

$ go list -m go.mongodb.org/mongo-driver

1.12.0

Describe how MongoDB is set up. Local vs Hosted, version, topology, load balanced, etc.

Atlas clusters (both sharded and replica sets)

The operating system and version (e.g. Windows 7, OSX 10.8, ...)

AL2

Security Vulnerabilities

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