We implemented a Yahoo! Address Book import in early 2011 using OAuth. My automated test starting failing sometime last week. (Best guess is 1/18/2011 but our instance of Jenkins isn't the best at keeping historical information.)
If I run my test with OOB for the callback_url everything works fine so I know it's not a problem with my API keys or the overall implementation. I'm using signpost-126.96.36.199 which follows the OAuth Core 1.0 Rev A spec so callback_url is passed during get_request_token.
Has something changed in the last week or so with Yahoo's OAuth implementation? Is there a page I can check with a revision history?