source:
  plugin: url
  data_fetcher_plugin: http
  data_parser_plugin: json
  authentication:
    plugin: basic
    username: ''
    password: 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'
  headers:
      Accept: 'application/json; charset=utf-8'
      Content-Type: 'application/json'
  urls: https://www.example.com/jsonfeed

public function getRequestHeaders() {
    return !empty($this->headers) ? $this->headers : [];
}

public function getRequestHeaders() {
      return !empty($this->configuration['headers']) ? $this->configuration['headers'] : [];
}