Lorna Mitchell has posted about her experiences with getting OAuth working with her PHP application by way of the PECL package that adds support into PHP.

I've been looking into OAuth recently and really like what I see, so I started looking at actually starting to play with something that uses it (and isn't twitter). In the pursuit of this, I spent some time walking through the process of how to actually authenticate using OAuth, as a client.

She briefly touches on the consumer key and secret and how those are passed along with the OAuth object creation to grab a request token, complete with details on setting a callback. She also mentions how to grab an access token - a piece of information you include in your API calls to let the remote service know who you are. All of her examples are using Yahoo! OAuth services.