To be able to access the proxy UI you need to ensure the SPS Agent is enabled and running so it can manage the authentication. You do not need to protect it with an external user directory if you do not need to, but you have to ensure the Agent is enabled as follows:
- Go to /secure-proxy/proxy-engine/conf/defaultagent folder.
- Edit WebAgent.conf file, and ensure EnableWebAgent parameter is set to Yes:
- Save changes and restart Access Gateway.