OK, I solved it.
Sorry for this.

Indeed i was using an older version of picketlink.
I just replaced PicketLink dependency versions by the newest one
<version.picketlink.javaee.bom>2.7.0.Beta1-20140731</version.picketlink.javaee.bom>
and it work.

Meanwhile, what should I do if I would like to use the picketlink module provided in Wildfly 8.1.0.Final - 2.5.2.Final - ?
Thanks for your support and your time.

KR
frederic