Hi,
curl is your way. Other option is using the Python REST SDK, https://github.com/tradel/AppDynamicsREST, and the Java flavor in https://github.com/Appdynamics/RestMetricQueries
Since usually we feed data from AppDynamics to view/analyze in other platforms like ELK (Elastic/Logstash/Kibana), the logstash http poller is our best friend, https://www.elastic.co/blog/introducing-logstash-http-poller.
Hope it helps, regards,
Luis