Fitbit Authentication Issue

[jyot]

I am developing an android application, where we integrated fitbit. We followed steps mentioned in below sample

https://github.com/Stasonis/fitbit-api-example-android

they are using implicit grant flow for authentication so we are getting only access_token not refresh token.

But in my application we require refresh token as well. So any have sample to implement authorization code grant flow

Thanks in advance