How to show a message if no attributes are released to SP?

[Tom Zeller]

> I'm looking for options that would allow an IdP to show the user a
> (error) message after authentication (and before user consent) in case
> no attributes would be released to the Service Provider or if another
> condition is met (e.g. a specific attribute is released).
> The message then should include a continue/abort option.
> 
> I there an easy way to configure this or would there be custom code
> needed for that? If so, where to best insert it?

Sounds like one option is a custom post-authn profile intercept flow to be run after attribute-release (which is also a profile intercept flow).