Till Klampaeckel's Blog: Yahoo: oauth_problem=consumer_key_rejected
During some of his work with the Yahoo! Search Boss API, Till Klampaeckel came across an issue with the OAuth connection causing an error of "oauth_problem=consumer_key_rejected" with his Zend Framework-based application.
The above process doesn't even take five minutes, but then I spent eight hours figuring out what oauth_problem=consumer_key_rejected means. Spent a couple hours googling, reading bug reports and even posted to the Yahoo! group associated with Search Boss. To cut to the chase: When you create a new project, it's not sufficient to just activate "Yahoo! Search Boss" (and provide billing details and so on).
His real issue was because of how Yahoo! apparently creates (or when they create) the OAuth connection information for you. He gives a two line example of how the Zend Framework can grab a OAuth token with Zend_Oauth. He goes on to talk about the OAuth implementation in PHP and how it's "pretty sucky" and that there's not much documentation around to help. He got things working, though, and included the sample code he used to make the connection - pulling the info from a an oauth.ini file, pushing the authentication parameters to the remote side, grabbing the headers and making the HTTP request with the OAuth information in place.