Google Search Appliance Connectors Administration Guide - Manual (Page 24)

You must include server.secure=true in the connector configuration before enabling
these stricter features.
To enable stricter security, perform the following steps by using the GSA Admin Console:
1. Click Administration > SSL Settings.
2. Make any of the following changes on this page:
a. Uncheck Enable HTTP (non-SSL) access for Feedergate.
b. Check Enable Client Certificate Authentication for Feedergate.
c. Check Enable Server Certificate Authentication.
3. Click Save.