Created on behalf of:

https://github.com/camunda/camunda-external-task-client-js/pull/65

In the latest Camunda version, there is a possibility to filter out the tasks that need to be fetched by specifying the values of the process variables: https://docs.camunda.org/manual/latest/reference/rest/external-task/fetch/

There is no such property in the request configuration object, so this property was added in this commit.