So I'm using this to talk to the Woocommerce REST API, and was having a lot of trouble figuring out what exactly $extra_parameters was supposed to look like (which WC REST API expects, besides being of the type OAUTH_AUTH_TYPE_URI).
The multidimensional array I fed it crashed PHP, so don't do that if you're in my shoes.
What ended up solving it was me looking through the OAuth source and noticing that $extra_parameters can also be a string, which, encoded as json (json_encode), solved all my troubles as WC accepted it.
