v0.9 - Token authentication

This release adds support for token authentication, a new upstream feature announced at WWDC 2016.

In the past, clients would authenticate to the server by providing a TLS certificate at connection time, and could send notifications only to the topics named in the client certificate. In practice, this generally meant that one client could only send notifications to a single app. With token authentication, a single client can send notifications to any topic (app) for which it has a valid signing key. This version of Pushy supports both TLS-based authentication and token authentication (though clients can only use one authentication strategy at a time).

For a complete list of changes, please see the v0.9 milestone.