client-api/src/main/java/com/streamsets/datacollector/client/ApiClient.java
public ApiClient addDefaultHeader(String key, String value) {
    defaultHeaderMap.put(key, value);
    return this;
  }
public ApiClient addDefaultHeader(String key, String value) {
    defaultHeaderMap.put(key, value);
    return this;
  }
Add a default header.

@param key The header's key
@param value The header's value