Retrieve a QR code login verification.
This API can be used from the unauthenticated browser that displayed the QR code to determine if a scanning device has completed the verification. The request must include the 'dsi' attribute to validate the caller is authorized to retrieve the verification.
If 'returnJwt' is 'true', the 'authnAnyUser' entitlement and an authenticated context are required.
NB: Once a verification's state has changed from PENDING, it will cease to exist after a given time.