Implement feedly API using Scribe

I am trying to implement Feedly API using Scribe.

For requesting the access token, they have an additional parameter grant_type to be included in the POST request to POST /v3/auth/token as documented in:

http://developer.feedly.com/v3/auth/

How do I take this into account?

The implementation of OAuth20ServiceImpl suggests that these it only submits these parameters:
* CLIENT_ID
* CLIENT_SECRET
* CODE
* REDIRECT_URI
* SCOPE

I am getting error that grant_type is null while calling getAccessToken because of this.