How can I efficiently track conversation history within a given session in a Dialogflow CX webhook, to use with external models like OpenAI’s GPT-4?

I can’t access the history parameter used for DialogFlow generators in this way: ${conversation USER:”Human:” AGENT:”AI”}. I’ve tried storing history as a string and using multiple parameter slots, but I encounter limitations. Is using contexts a viable solution, or are there other methods? Any examples or suggestions would be appreciated.