please try to login to the IM Web GUI and connect to the MDM from the Maintain Tab.
If displays a certificate warning, you should be able to add it to the gateway's keystore.
Im wondering what the "localhost_access_log.log" shows
can we try the CURL command below?
curl -k -v --basic --user admin:<PASSWORD> https://<GATEWAY IP>/api/login
Im also wondering if when you try the CURL command using the gateway with which you installed the ScaleIO system,
if your able to get a key(token) in the HTTP response.
basically seen this in an instance from https://community.emc.com/message/992052?et=watches.email.thread#992052
two options: one is to use the insecure option for CURL
-k, --insecure (SSL) This option explicitly allows curl to perform "insecure" SSL connections and transfers. All SSL connections are attempted to be made secure by using the CA certificate bundle installed by default. This makes all connections considered "insecure" fail unless -k, --insecure is used.
The other is to get a properly signed and trusted certificate (preferably with your own PKI) into ScaleIO, so you can trust it.