How to generate a SAS token for notification hubs

Hello

I want to register a Android device on the Windows Azure Notification Hub. The documentation provides one small example at http://msdn.microsoft.com/en-us/library/dn495631.aspx, but does not explain how generating a SAS token. It's using a function getSelfSignedToken. How can I implement this function?

It's really hard to use this without a SDK since there is almost no documentation on how to use the REST API. 

Thanks,
Roland