postiz-app: Forged signed tokens let any registered user take over other users and organizations

Postiz signs its session, invitation and password reset tokens with one shared secret and without any marker of what a token is for. A route that refreshes the credentials of a browser-extension channel signed data taken from the request itself and stored the result where the requesting user can read it back. A user could therefore obtain a validly signed token containing any claims they choose, which the application accepts as a session, as an organization invitation with a chosen role, as a password reset or as an enterprise provisioning token.

A second, narrower route that creates team invitations signs extra fields from the request body in the same way.