Example RSG application Authentication+and+Linking ?

I think the closest one is the signup sample channel - that has keyboard entry for an email address so it's a good start?

https://roku.box.com/s/puqgslcujkt364cfit7a4zwx1hfps5ew

See https://sdkdocs.roku.com/display/sdkdoc/Roku+Billing+and+In-Channel+Purchasing#RokuBillingandIn-ChannelPurchasing-Testingthein-channelproductandsamplecodeoverview

If you require a linking code or email verification or something else that needs to be chunked in.