Add the ability to refresh OAuth tokens

[innocenzi]

See: https://oauth2-client.thephpleague.com/usage/#refreshing-a-token

[iamdadmin]

Awesome, I actually need this, could you also expose the token itself as well as the refresh_token so that also can optionally be stored to use for making outbound calls in apps that need that?

[innocenzi]

@iamdadmin this is already possible if you use requestAccessToken directly