How should an application add/remove scopes to an existing grant?
Sorry, you can't do that. You will need to re-authorize the user. I agree that it would be nice to incrementally add scopes, but you will still need to show an authorization page, so I think you won't gain much doing that.
Tried adding additional scopes using oauth2client's OAuth2DecoratorFromClientSecrets via the scopes parameter.
I believe users of an application would prefer to gradually expand privileges; as its needed, and as trust forms...
What is the best way to add/expand/remove scopes when the application has an existing grant? Revoke and reauthorize?