[Resolved] Manually decode Stateless Session cookie

I need to be able to decode a Stateless session cookie manually (not across silhouette) but I not find how to do it.
When i see the code (in SessionAuthenticatorService.retireve), the only thing I see is the value of Cookie is encode in Base64 from a json that can be mapped to SessionAuthenticator type.
When i pick a cookie session built from my play app, i retrieve this kind of thing :

when i try to Base64 decode the = right part that thow an java.lang.IllegalArgumentException: Illegal base64 character 2e

Can you help me plz ? Thx.

Ok i find that play encode the session cookie with play secret.
Do you know where i can find the algo to decode this plz ?

Ok i find the good way.