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This is still supported, but with a few exceptions, a better approach in V4 is to rely on a common set of encoding rules contained in the new AttributeRegistryConfiguration based on reasonable conventions for the names of the IdPAttribute objects. For example, if you just accept that you should put the subject's e-mail address into an IdPAttribute called "mail", then the registry knows how to encode that into SAML automatically using the name prescribed by the standard.
Configuration
In a typical (and default) configuration, only one configuration resource is supplied for controlling attribute resolution, a file called attribute-resolver.xml. All such resources must contain a "root" element named <AttributeResolver> defined in the urn:mace:shibboleth:2.0:resolver XML namespace.
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All of the examples shown assign attribute IDs that correspond to pre-existing encoding rules from the default supplied registry.
The resolver configuration itself consists of an unordered set of <AttributeDefinition> and <DataConnector> elements that are of various types. These plugins to the actual work and most of the documentation can be found under those two headings.
Simple attribute-resolver.xml file
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