public function setAuthnContextDecl(Chunk $authnContextDecl) : void
    {
        if (!empty($this->authnContextDeclRef)) {
            throw new \Exception(
                'AuthnContextDeclRef is already registered! May only have either a Decl or a DeclRef, not both!'
            );
        }

        $this->authnContextDecl = $authnContextDecl;
    }