...
Generally speaking, development of most extensions can be done via Maven without actually downloading and importing projects for from the Shibboleth code base. In some cases, particularly where development of web flows is concerned, it is typically easiest to import at least some of the projects in order to run a "testbed" project developed alongside the IdP to exercise flows in a real world environment.
Development other than via maven is not addressedsupported.
Maven Artifacts
The Maven coordinates for Shibboleth code artifacts can be found by browsing or Nexus release repository. Selecting a particular "jar" artifact will display the Maven dependency content required to insert. It's advisable to specify IdP or OpenSAML versions corresponding to the lowest minor version you need to support in your extension.
As multi-module projects, both OpenSAML and the IdP contain a large number of individual artifacts, and your dependencies will be directly to the specific API modules you need, not to a the "whole" project. Per the Java Product Version Policy, you should not be establishing non-test dependencies on Implementation modules containing only implementation classes unless you're prepared to give up compatibility assumptions across versions. Classes in those modules Implementation classes can change incompatibly, even in a simple patch.
...