How to access incoming OAuth Token?

I have a API - lets say API A, which will call Agent (Foundry Hosted Agent).

The Agent code is the most basic written using python agent framework and uses Hosting Adapter, it has a chatClient as agent - and uses - from_agent_framework(agent).run()

This Agent must call another API, lets say API B which requires OAuth token as well, but this OAuth must be a OBO (on-behalf-of token) to preserve initial API A user identifier in original token.

To create a OBO token, Agent A will require to get access to token sent in Authorization Header otherwise how will it create OBO using original incoming token.

So, in Agent A, how do I access the original OAuth Token in agent_framework?

Thanks.