tvOS authorization support.

– Implements Google's OAuth 2.0 for TV and Limited Input Device Applications flow, https://developers.google.com/identity/protocols/OAuth2ForDevices
– This is the same authorization flow used by the YouTube TV app (https://www.youtube.com/tv).
– The flow is based on, but not fully compatible with the IETF draft protocol specification https://tools.ietf.org/html/draft-ietf-oauth-device-flow

Author: WilliamDenniss

Example-tvOS/.gitignore

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+## Build generated
+build/
+DerivedData/
+
+## Various settings
+*.pbxuser
+!default.pbxuser
+*.mode1v3
+!default.mode1v3
+*.mode2v3
+!default.mode2v3
+*.perspectivev3
+!default.perspectivev3
+xcuserdata/
+
+## Other
+*.moved-aside
+*.xcuserstate
+
+# Pods are ignored in the samples as all Pods & their dependencies are either
+# development Pods (this repo) or sourced from repos in the same organization.
+# Generally we recommend versioning Pods, see the pros & cons here:
+# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
+Pods