Unrecognized SSL message, plaintext connection?

Symptoms

The client logs the following error:

ERROR: login failed: CTGES0008E
The Authentication Client received a fault from the Authentication Service. Fault reason:

"javax.net.ssl.SSLException: Unrecognized SSL message, plaintext connection?"

fault.getCodeLocalPart = Server.userException
fault.getCodePrefix =

Causes

The authnServiceURL configuration property in the ibmessclientauthncfg.properties file identifies the use of HTTPS, but points to a non secure port on the host computer.

Resolving the problem

Fix the property to point to a valid and functioning Authentication Service.