changed session fixation mode

Required to get sessions working even between switching kernels, however I am not sure if we introduce a new security issue with that

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| Tests pass?   | yes
| Fixed tickets | none
| Doc           | none