Signed image URL's are 404-ing


For about a year, we’ve used Twitter4j to sign links to images inside of DM’s, such that the image will load in a browser even if the user is not currently logged in to Twitter.

An example of such a link:

It appears that sometime between 2015-04-04 and 2015-04-06, these signed links stopped working consistently. Our code hasn’t changed during this period.

Is this the result of a recent Twitter change? Is there a workaround we can employ to get our application working again soon?