class OmniAuth::Strategies::Realme::RealmeAuthnFailedError
Create an exception for each documented Realme
error (developers.realme.govt.nz/how-realme-works/realme-saml-exception-handling/).
All the errors we raise inherit from `OmniAuth::Strategies::Realme::Error` so a caller can rescue that if they want to rescue all exceptions from this class.