Missing support for "approval_prompt"

[alextekartik]

Currently, as seen the in the example, there is no way to "switch" to a different account after logout.
One basic option would be to support "approval_prompt": "force" in the _getAuthorizeUri (checked locally)

[mpost]

+1

[alextekartik]

I forked the project, did the proposed change and created a pull request