...
You may also dynamically derive the path to use, typically so that it can vary based on aspects of the request, by defining a bean named shibboleth.authn.External.externalAuthnPathStrategy of type Function<ProfileRequestContext,String>.
The shibboleth.authn.External.ClassifiedMessageMap is a map of exception/error messages to classified error conditions. You can make use of this map either by modifying it to understand the error or exception messages returned by your external code.
...