How do I submit and process request params with an Oauth request?
It's not really clear to me what you want to achieve. What are the "extra" fields, and why don't you derive the fields from the user's profile directly?. About 98% of the FB Login implementations I've seen just use the "Login with Facebook" button and get the user's data during the OAuth process itself, and not manually entered by the user.
With passport-facebook for example, it's possible that you
a) Configure custom scopes
b) Enrich the profile object with the custom scope's data
The profile object will then contain the additional requested fields automatically, and you don't need to tweak the request object itself.