So I figured out the answer after copious amount of Googleing and grasping a better understanding of both the Withings API and the OAuth library I was using. Basically Withings uses query strings to pass in API parameters. I though I was going about passing these parameters correctly when I was making API calls, but apparently I needed to explicitly set the OAuth library to use the query string scheme, like so
http_method: :get, scheme: :query_string
This is appended to my OAuth consumer configuration and all worked fine immediately.