Secret rotation

[HeikoMueller]

Hi... I have a question. In an earlier commet you mentioned that you'd add a way to rotate the secret by introducing old_secret:

#2 (comment)

I was unable to find this in the code. Has the idea of rotating secrets been implemented. If not, how would you approach this?

Thanks!

[HeikoMueller]

I added a pull request as a suggestion on how to tackle this:
#23