Resume Polling after Restart

[paulmccarron]

• Store access token encrypted in data store
• Update access token in database when Spotify Client refreshes token
• When Spotify Playlist Janitor starts up, check data store for access token, decrypt, try and user refresh token, instantiate new Spotify Client if refresh successful, clear access token in data store if unsuccessful
• Add tests of new methods and services

[paulmccarron]

Encrpty/Decrypt: https://www.c-sharpcorner.com/article/encryption-and-decryption-using-a-symmetric-key-in-c-sharp/