PicketLink should have all necessary XSDs stored local. User may experience some issues in case a site with missing XSD is down.

Running PicketLink picketlink (unit) tests offline causes some failures.

The first step to fix the issue could be to fix !DOCTYPE header of modules/federation/src/main/resources/schema/w3c/xmldsig/xmldsig-core-schema.xsd and modules/federation/src/main/resources/schema/w3c/xmlenc/xenc-schema.xsd. There should be XMLSchema.dtd instead of http://www.w3.org/2001/XMLSchema.dtd (have not found exact reason).

The second step is to add missing schemas to modules/federation/src/main/resources/schema/ and to add related mapping to IDFedLSInputResolver.
I.e. to add http://docs.oasis-open.org/xacml/2.0/access_control-xacml-2.0-context-schema-os.xsd and http://docs.oasis-open.org/xacml/2.0/access_control-xacml-2.0-policy-schema-os.xsd schemas and mappings.

There are some other failures to investigate.