Jenkins Pipelines: How to use withCredentials() from a shared-variable script - jenkins

Question

I'd like to use a withCredentials() block in a shared-variable ("vars/") script rather than directly in the Jenkins pipeline because this is a lower-level semantic of a particular library, and also may or may not be required depending on the situation. However, withCredentials (or, at least, that signature of it) doesn't appear to be in scope.
script:
def credentials = [
[$class: 'UsernamePasswordMultiBinding', credentialsId: '6a55c310-aaf9-4822-bf41-5500cd82af4e', passwordVariable: 'GERRIT_PASSWORD', usernameVariable: 'GERRIT_USERNAME'],
[$class: 'StringBinding', credentialsId: 'SVC_SWREGISTRY_PASSWORD', variable: 'SVC_SWREGISTRY_PASSWORD']
]
withCredentials(credentials) {
// ...
}
Console:
hudson.remoting.ProxyException: groovy.lang.MissingMethodException: No signature of method: BuildagentInstallAndRun.withCredentials() is applicable for argument types: (java.util.ArrayList, org.jenkinsci.plugins.workflow.cps.CpsClosure2) values: [[[$class:UsernamePasswordMultiBinding, credentialsId:6a55c310-aaf9-4822-bf41-5500cd82af4e, ...], ...], ...]
Has anyone had any success with this?

Answer 1

I'm using a shared library rather than a shared variable, but I guess it is a similar situation.
I'm not using the $class parameter, but i'm calling directly one of the functions suggested by the pipeline snippet generator. You can have a list here. In the example below, I use the usernameColonPassword binding.
In the pipeline, I instantiate the class utilities and I pass this to the constructor. Then, in the library, I use the step object to access the pipeline steps (such as withCredentials or usernameColonPassword).
class Utilities implements Serializable {
def steps
Utilities(steps) {
this.steps = steps
}
def doArchiveToNexus(String credentials, String artifact, String artifact_registry_path){
try {
this.steps.withCredentials([steps.usernameColonPassword(credentialsId: credentials, variable: 'JENKINS_USER')]) {
this.steps.sh "curl --user " + '${JENKINS_USER}' + " --upload-file ${artifact} ${artifact_registry_path}"
}
} catch (error){
this.steps.echo error.getMessage()
throw error
}
}
}

Answer 2

You can try following:
import jenkins.model.*
credentialsId = '6a55c310-aaf9-4822-bf41-5500cd82af4e'
def creds = com.cloudbees.plugins.credentials.CredentialsProvider.lookupCredentials(
com.cloudbees.plugins.credentials.common.StandardUsernameCredentials.class, Jenkins.instance, null, null ).find{
it.id == credentialsId}
println creds.username
println creds.password
But it is not secure, everything will be in console log

Answer 3

I was able to obtain credentials inside the shared library with proper passwords masking with such code:
class Utilities implements Serializable {
def steps
Utilities(steps) {
this.steps = steps
}
def execute() {
this.steps.withCredentials(
bindings: [
this.steps.usernameColonPassword(
credentialsId: this.credentialsId,
variable: "unameColonPwd")
]) {
this.steps.sh "echo {this.steps.env.unameColonPwd}"
}
}