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New installs load a default set of rules from conf/attributes/default-rules.xml to use for a common/standard set of attributes, this . This contains rules for encoding and decoding of common attributes.
Additionally the configuration loads conf/attribute-resolver.xml. The default resolver does not specify any attribute encoders, but importing referencing the file allows use of encoders for exceptional cases if you prefer to use them.
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Upgraded systems with an older services.xml file are configured internally to load only conf/attribute-resolver.xml the existing AttributeResolverConfiguration resources in order to process the <AttributeEncoder> elements within it in order to produce a compatible set of rules to use. The default set of rules supplied with the software is not loaded in order to prevent any changes in behavior, including duplication of encoded attributes.
The default resource set after upgrades is meant as a compatibility baseline. Once a determination on the desired approach to configure behavior in the future is made, upgraded systems can be adjusted to add in a shibboleth.AttributeRegistryResources bean and an explicit decision made as to what resources to load by editing services.xml to do so.
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