Gets a specified playback authorization key pair and returns the <code>arn</code> and <code>fingerprint</code>. The <code>privateKey</code> held by the caller can be used to generate viewer authorization tokens, to grant viewers access to private channels. For more information, see <a href="https://docs.aws.amazon.com/ivs/latest/userguide/private-channels.html">Setting Up Private Channels</a> in the <i>Amazon IVS User Guide</i>.