A promise that resolves to a tuple.
The first element is either an AccessTokenForConnectionError if an error occurred, or null if the request was successful.
The second element is either null if an error occurred, or a ConnectionTokenSet object
containing the access token, expiration time, and scope if the request was successful.
Exchanges a refresh token for an access token for a connection.
This method performs a token exchange using the provided refresh token and connection details. It first checks if the refresh token is present in the
tokenSet. If not, it returns an error. Then, it constructs the necessary parameters for the token exchange request and performs the request to the authorization server's token endpoint.