Support for Front Channel SLO requests

[bpalme]

Hi I'd like to put in a vote for support for service definitions that use Front Channel (GET instead of POST) SLO requests. See:

https://apereo.github.io/cas/6.2.x/installation/Logout-Single-Signout.html#single-logout-per-service

Currently it appears that the Client only looks for logout requests coming in as a POST param.

Thanks!
Brent

[prigaux]

For the record,

a sample front channel SLO request submitted by CAS resembles the following format:

curl 'https://service.url?callback=jQuery112409319555380089843_1509437967792&logoutRequest=[BASE64 encoded request]&_=1509437967793'

Front-channel is especially nice since the user provides the application session cookie... but nowadays JSONP is bad choice because of blocked third-party cookies 😢. So back-channel SLO seems to be the best choice at the moment.