Adds a video to the YouTube playlist whose ID is stored in the passed Credentials.
Request OAuth API tokens from Google.
Refreshes the OAuth API token in the passed Google credentials.
Requests a Google API authorisation code from Google servers, then uses it to obtain an access key and a refresh OAuth key.
Validates a Google OAuth token, returning the JSON received from the server.
Bits and bobs to get Google API credentials and for YouTube playlist management.