I am also working on the same thing. Please ensure that you have given proper API permission in Azure for the botframework app, as shown below (add/remove permission based on your requirements):
Follow the documentation Get Teams specific context for your bot - Teams | Microsoft Learn to get the required details.
You can either fetch the details in your custom action before calling your other APIs or set the fetched MS Teams credential information as slot values at the beginning of chat (e.g., greet intent) to avoid redundant info calls from MS Teams.
The other and bit smarter way of doing it would be to customize the rasa botframework connector and implement the fetching and persisting of the credential information from MS Teams at the initiation of the conversation.