Backchannel logout not working due to invalid client session note set

[malinowskij]

After many tests I am unable to trigger backchannel logout.

I have debugged the plugin code and have come to the following conclusions:

1. In the CASLoginProtocol class, the tickeet is retrieved from the client session notes
2. However, during validateService the ticket is set with the ticket prefix key, i.e. "ST-", instead of "service_ticket" (AbstractValidateEndpoint:154)

Looking at the commit history, you can see the change:

This causes serviceTicket to always be null.

[Stelmach83]

@jacekkow please take a loot at this