Returns an auth_url that the frontend must redirect the user to in order to
grant TrueLayer access to their bank account. The state parameter is set to
the authenticated user’s ID.
Bearer authentication header of the form Bearer <token>, where <token> is your auth token.
Comma-separated list of TrueLayer provider IDs to show (e.g. lloyds,barclays).
Omit to show all supported banks.