The trial system uses the same IDP as SCN. Inside a web browser both support the username/psw and SSO authentication. For command line tools only user/password is supported. This is different to the SAP_ALL password.
Try the URLs below to access the login screen if you suppress sending your certificate by the browser, then you can use both "register" and/or "forgot password" functions:
https://account.hanatrial.ondemand.com/cockpit
or just use this:
https://www.sdn.sap.com/irj/scn/forgotpassword