Swagger-codegen: [JavaScript] How do I set auth headers for all/some requests?

Description

I generated a JavaScript SDK, but am not clear on how to set authentication headers. I'd love to be able to set the auth headers used for all future requests via some sort of default headers setting. I've tried setting the ApiClient.defaultHeaders like below, but with no success:

Update: I updated the below code showing a way I got the headers to be added to the requests made by connAPI, but this code is definitely less than ideal. There must be another way to set these auth headers in a more flexible/programmatic way.

import telnyxSDK from 'telnyx-sdk';

const connAPI = new telnyxSDK.ConnectionsApi();
connAPI.apiClient.defaultHeaders = {
  'x-api-user': 'my-username',
  'x-api-token': 'my-token'
};

let _payload = {
  connection_name: 'test-name',
  tech_prefix: 'test-prefix',
  active: true
};

return connAPI.addConnection(_payload).then(function(data) {
  console.log('API called successfully. Returned data: ' + data);
}, function(error) {
  console.log(error);
});

The request gets made, but without any of the auth headers.

Please advise, thanks!

Swagger-codegen version

2.2.3 (via swagger-codegen-cli docker image)

Swagger declaration file content or url

https://api.telnyx.com/mission_control_docs

Command line used for generation

swagger-codegen generate -i https://api.telnyx.com/mission_control_docs -l javascript