Using AWS credentials is such a common task that CircleCI has a special section for it in each project's configuration. If you navigate to Permissions | AWS Permissions, you'll find two fields for your AWS Access Key ID and AWS Secret Key. Setting these here ensures you'll never need to check them into source control and that any AWS libraries you use (noted in the following screenshot) will automatically pick up the values as environment variables.
Setting these credentials in this section works as we would expect for the Serverless framework, allowing any serverless command to execute successfully provided the keys we attach have the correct IAM permissions:
