Question: I'm trying to implement pre-authorization for google wallet purchases for an android application. Google has [a page describing this feature](https://developers.google.com/wallet/instant-buy/preauth), but the instructions stop after obtaining a api client ID; no code samples on how to initiate the request.

The API has [references to checking the status](https://developer.android.com/reference/com/google/android/gms/wallet/Wallet.html#checkForPreAuthorization%28com.google.android.gms.common.api.GoogleApiClient,%20int%29) of pre-authorization, but again nothing about how to request it.

Can anyone point me to a code sample or api call I'm missing?

Answer: 
(I work at Asana.) This is a very good question. Asana has actually been working on a subscriptions endpoint for the API, and has alpha-tested a version in the past. Finishing it up and launching it are on the near-term roadmap so in all likelihood you will hear something about it in the next few months.
Asana now has beta support for webhooks which can "allow an application to be notified of changes" which can do away with polling:

* <https://asana.com/developers/feed/webhooks-beta>
* <https://asana.com/developers/api-reference/webhooks>

This is in addition to (and in a sense based on) "Events" mentioned in the comments.