Enable OAuth2 authentication support

Packages describing “oauth” as local USE flag

Package “oauth” Flag Description
mail-client/claws-mail Enable OAuth2 authentication support
sci-geosciences/viking Enable OAuth authentication for OSM
x11-wm/xpra Enable OAuth2 authentication in the server
dev-ruby/faraday_middleware Include FaradayMiddleware::OAuth
gnome-extra/evolution-data-server Enable internal OAuth2 authentication support for Google and Outlook.com. If gnome-online-accounts is enabled and used, this is not necessary, but both can be supported at the same time with different setup at runtime

All packages providing a “oauth” USE flag (3)