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Handling this situation well is dependent upon having enough information to lead the user to a resolution of the problem (or a determination that the IdP in question simply won't allow itself to be used for the SP in question). Simply telling the user that some list of attributes has to be supplied is not going to help, particularly if that list is overly technical in nature (e.g., a user will not in general know what an "EPPN" is). Even if the IdP organization has a process for dealing with attribute release, most users are not going to know anything about it. Rather, a contact at the IdP will often need to manage this process and deal with technical matters on behalf of the affected user(s).
For general information about addressing other types of errors, see Error Handling.
Leveraging the Error Handling URL
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