The lib/lti1p3 library now passes $options['form_params'] instead of
$options['body'] when making access token requests. To maintain the
'application/x-www-form-urlencoded' content-type required by OAuth 2.0
(https://www.rfc-editor.org/rfc/rfc6749#section-4.1.3), the client has
been changed to convert these array params into a body query string,
which matches the behaviour prior to the library upgrade and makes
the tool can continue to call tool platform services. Support for
$options['body'] remains, as this is still used during service calls.