OAuth2 Tokens from providers that don't provide an expiry date are incorrectly expired on first use

I've been trying to use the Online Accounts system to manage log in to the SoundCloud web site, and hit a problem: I can sign in without problem through the control panel, but when I try to retrieve the token via libsignon-glib, I get an error and the account is marked as signed out.

Looking at the syslog chatter from signond, it apparently decides that the token has expired:

    May 5 14:11:50 scruffy signonpluginprocess[7357]: oauth2plugin.cpp 206 respondWithStoredToken : Stored token is expired

This was a bit surprising, since SoundCloud says their tokens are not set to expire. Looking furtherback to where the token was stored, I see:

    May 5 14:10:03 scruffy signonpluginprocess[7263]: oauth2plugin.cpp 631 storeResponse : QMap(("REDACTED_CLIENTID", QVariant(QVariantMap, QMap(("Expiry", QVariant(int, 0) ) ( "Scopes" , QVariant(QStringList, ("non-expiring") ) ) ( "Token" , QVariant(QString, "REDACTED_TOKEN") ) ( "refresh_token" , QVariant(QString, "") ) ( "timestamp" , QVariant(uint, 1399270203) ) ) ) ) )

In particular, Expiry==0. This seems to be the code where the expiry is set, where it reads the "expires_in" property from the response JSON:

    http://code.google.com/p/accounts-sso/source/browse/src/oauth2plugin.cpp?repo=signon-plugin-oauth2#444

However, looking at the SoundCloud HTTP API reference, it isn't sending this in their JSON response:

    http://developers.soundcloud.com/docs/api/reference#token

It looks like this method needs to check whether expires_in is actually included in the JSON response.