challenge Reference Id
Returns the challenge's Reference ID. This value will appear in the challenge screen. The value is unique per app run. Meaning, for each challenge in the app run the value will be the same for all challenges. Note that the value in the challenge screen will be different from the returned value when:
The Doctor App is enabled, due to internal implementation.
The "X-PX-AUTHORIZATION" HTTP header is missing or does not contain a token.