Error info: Auth config in endpoint config without the scheme listed

[jdisanti]

This is additional context for the error message:

failed to select an auth scheme to sign the request with. "<auth scheme>" wasn't a valid option because there is auth config in the endpoint config, but this scheme wasn't listed in it.

If you saw this while using the AWS SDK, then this is a SDK bug and you should file it in the aws-sdk-rust repository.

Otherwise, if you're using smithy-rs to generate clients, then this is a modeling issue. The endpoint rule set for the service has auth config in it that may hold config for other auth schemes, but is missing config for this specific auth scheme. Add the config to resolve this.