Currently the provider allows configuration for secrets manager for the API key, however it looks like only static AWS credentials can be used which require assuming a role first and exporting environment variables. It would be much cleaner if you could support shared profiles, much like the AWS provider does https://registry.terraform.io/providers/hashicorp/aws/latest/docs#profile-1.
https://docs.aws.amazon.com/sdk-for-go/v1/developer-guide/configuring-sdk.html
Specifically https://github.com/mongodb/terraform-provider-mongodbatlas/blob/master/internal/provider/credentials.go#L49 is static credentials, but would be great to add profile as an option as well.