On an AMS managed instance SSL/TLS is terminated at the ELB. So they install a local SSL certificate when going to the Author / Publish IP. HTTP access via port is locked down heavily.
Options
- work with your CSE to whitelist your IP so you can hit the Author over http://<Ip>:4502
or
- connect over https as you are doing and tell maven to use a flag like : -Dmaven.wagon.http.ssl.insecure=true