Re: oauth2 support for Emacs email clients

[Gregory Heytings]

> Upon authentication, oauth2.el does not support `access_type=offline'. 
> It is my understanding that this is needed to get upon authorization not 
> only an access token, but also a refresh token.  The latter is needed to 
> grant an app continuous access beyond the short lifetime of an access 
> token.

Your understanding is correct, except that AFAIK it is not "needed", at 
least not in general.  But of course as you might guess each provider 
implemented their own variant / extensions of the OAuth protocol.  If you 
need these parameters in your case, you can add them in 
oauth2-request-authorization.

> However, the emacs url machinery also lacks the code that is needed to 
> use the referesh token in order to request a new access token if the 
> current access token has expired.

This should work AFAIU; I don't use oauth2.el myself, but a comment says 
"If the token needs to be refreshed, the code handles it automatically and 
store the new value of the access token", and that refreshing mechanism is 
an essential part of OAuth, if it is not present OAuth is not usable.