Dropbox OAuth2 grant type not supported

[lzaiko]

Hi there.
I wanted to use the oauth2_client with the Dropbox Oauth2 api. But it seems that the client in restricted to only two 'grant_type' (azure_client_credentials and client_credentials), while the dropbox api uses "authorization_code" as 'grant_type' https://www.dropbox.com/developers/documentation/http/documentation#oauth2-token
Is it possible to integrate the 'grant_type' fro Dropbox or at least let users to be free to use their own 'grant_type' in token retrieving request.

Thanks