add_global_pipeline_library.groovy

//Example: run_groovy_script.sh ../wendy.ini add_global_pipeline_library.groovy <owner> <repo> [<branch> <ssh credentials id> <scan credentials id>]
import jenkins.model.*
import org.jenkinsci.plugins.workflow.libs.*
import org.jenkinsci.plugins.github_branch_source.*
import jenkins.scm.api.mixin.ChangeRequestCheckoutStrategy

String owner             = args[0]
String repo              = args[1]
String branch            = args.size() > 2 ? args[2] : 'master'
String sshCredentialsId  = args.size() > 3 ? args[3] : 'jenkinsgithub'
String scanCredentialsId = args.size() > 4 ? args[4] : 'githubjenkins'

def inst = Jenkins.getInstance()
def desc = inst.getDescriptor("org.jenkinsci.plugins.workflow.libs.GlobalLibraries")

GitHubSCMSource source = {
    GitHubSCMSource _source = new GitHubSCMSource(owner, repo)
    _source.setCredentialsId(scanCredentialsId)
    _source.traits.add(new BranchDiscoveryTrait(true, true));
    _source.traits.add(new OriginPullRequestDiscoveryTrait(EnumSet.of(ChangeRequestCheckoutStrategy.HEAD)));
    _source.traits.add(new ForkPullRequestDiscoveryTrait(EnumSet.of(ChangeRequestCheckoutStrategy.HEAD), new ForkPullRequestDiscoveryTrait.TrustContributors()));
    _source.traits.add(new SSHCheckoutTrait(sshCredentialsId));
    return _source
}()

SCMSourceRetriever retriever = new SCMSourceRetriever(source)

LibraryConfiguration libconfig = new LibraryConfiguration(repo, retriever)
libconfig.setDefaultVersion(branch)
libconfig.setImplicit(false)
desc.get().setLibraries([libconfig])