@Dimitri: I tried exactly that yesterday and I can confirm ist works. After setting log level to debug (got not really more info though), and quadruple checking every setting I thought well, maybe it is a bug. Hence downgraded and it tada, works.
Seems there is a bug in the current version of openid.
@christi...[at]
shop-apotheke.com, for the quick fix, just downgrade to the previous version. Not sure if there are any security concerns, I did not check the release notes but i am also not using it for production.
Maybe someone from RCDevs could comment and/or take a look into that.
Best,
Matthias