elasticsearch/x-pack/plugin/security/lib/build.gradle

// This build deserves an explanation. Nimbus-jose-jwt uses gson internally, which is unfriendly
// to our usage of the security manager, to a degree that it makes the library extremely difficult
// to work with safely. The purpose of this build is to create a version of nimbus-jose-jwt with
// a couple classes replaced with wrappers which work with the security manager, the source files
// in this directory.

// Because we want to include the original class files so that we can reference them without
// modification, there are a couple intermediate steps:
// nimbus-jose-jwt-modified-part1: Create a version of the JAR in which the relevant class files are moved to a different package.
//      This is not immediately usable as this process rewrites the rest of the JAR to "correctly" reference the new classes. So, we need to...
// nimbus-jose-jwt-modified-part2: Create a JAR from the result of part 1 which contains *only* the relevant class files by removing everything else.
// nimbus-jose-jwt-modified: Use the result of part 2 here, combined with the original library, so that we can use our
//      replacement classes which wrap the original class files.