How to get an access token for the federated API from Cognito User Pool

Question

I'm using an AWS Cognito User Pool. I have setup an identity provider. Let's say Facebook.

I am able to login, and I see the user appear in the user list.

Now, I want to be able to make requests to Facebook API using the access token on behalf of the user.

How do I get this access token?

I can only seem to get the Cognito's access token, which, of course, does not work for Facebook.

Thanks!