Default credentials provider does not fall back to process.env as the documentation states

[Steve Green]

You can also pass AWS credentials in explicitly (otherwise taken from process.env)

  } else {
    credentialsProvider = new SimpleCredentialsProvider(credentials);
  }

Assuming this should be:

  } else {
    credentialsProvider = new SimpleCredentialsProvider({
        accessKeyId: process.env.AWS_ACCESS_KEY_ID,
        ...
    });
  }

[Steve Green]

My apologies.. that does happen but later in the code.