Take user session info from Teams activity objects, to enable usage of user session tokens for permissions

I understand from the documentation that Member credentials are not supported on downstream channels, such as MS Teams which are we are interested in using.

When a user accesses an agent via Teams, there is no capability to sign in via the OAuth connector as is on the WatsonX Orchestrate test chat. This makes sense because it would be expected that the user's session, referenced in the Activity Objects between Teams and WXO would be already stored and could be usable for identifying users and determining permissions.

However, this is not stored within a connections object, and therefore we cannot access that session information. This code works for getting the access token from an OAuth session within the WXO test chat:

def _get_mcp_client() -> Client:
"""Creates an MCP client with Bearer token authentication from the OAuth connection.

Zero-trust model: OAuth token validated on every request by the MCP server.

Returns:
Client: FastMCP client configured with the user's OAuth token
"""
oauth_conn = connections.oauth2_auth_code(OAUTH_APP_ID)
token = oauth_conn.access_token

print(f"[MCP] Connecting to: {MCP_SERVER_URL}")
print(f"[MCP] Bearer token preview: {token[:20]}...")

transport = StreamableHttpTransport(MCP_SERVER_URL)
return Client(transport, auth=BearerAuth(token=token))

However, that oauth2_auth_code connection object is inaccessible in Teams, and therefore we cannot pass the user details anywhere to provide context for permissions. If a user chat requests an OAuth sign in normally in the WXO test chat, it shows nothing in Teams to prompt the user, but should instead have a way to access these credentials.