title: Can I use AWS SNS in iOS app without Cognito
body: <p>I'm building an app and want to leverage AWS SNS for the push notifications. The documentation seems a bit spars.
  I'm not using Cognito, and at the stage where I have got the deviceToken from Apple, the hasn't been a login in any case. The app uses AppAuth for the authorisation.</p>
  <pre><code>let defaultServiceConfiguration = AWSServiceConfiguration(
          region: AWSRegionType.USEast1, credentialsProvider: nil)
      AWSServiceManager.default().defaultServiceConfiguration = defaultServiceConfiguration
  </code></pre>
  <p>Obviously 'nil' doesn't work as credentialProvider. Is there anything I can give there to satisfy AWS?</p>