I'm trying to run a ssh deployment using jenkins and the SSH Pipeline Steps plugin. I've created a ssh key using openssh on MacOS.

ssh-keygen -m PEM

Then I copied the key to remote server using ssh-copy-id. The login with my command line works well. In Jenkins I created a new secret.

My pipeline step looks like this

stage("Deploy to docker host") {
    steps {
        script {
                withCredentials([sshUserPrivateKey(
                credentialsId: "docker-jenkins", 
                keyFileVariable: 'sshKey',
                usernameVariable: 'sshUser'
            )]) {
                def remote = [:];
                remote.name = 'docker-host';
                remote.host = '127.0.0.1';
                remote.user = sshUser; 
                remote.identity = sshKey;
                remote.allowAnyHosts = true;

                sshCommand remote: remote, command: "ls -lrt"
            } 
        }
    }
}

When I run the pipeline I get the following output.

Executing command on 01-de.docker[127.0.0.1]: ls -lrt sudo: false

com.jcraft.jsch.JSchException: invalid privatekey: [B@4ba138bd
    at com.jcraft.jsch.KeyPair.load(KeyPair.java:747)
    at com.jcraft.jsch.IdentityFile.newInstance(IdentityFile.java:46)
    at com.jcraft.jsch.JSch.addIdentity(JSch.java:441)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoCachedMethodSite.invoke(PojoMetaMethodSite.java:192)
    at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56)
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:149)
    at org.hidetake.groovy.ssh.connection.UserAuthentication$Trait$Helper.configureUserAuthentication(UserAuthentication.groovy:39)
    at org.hidetake.groovy.ssh.connection.UserAuthentication$Trait$Helper$configureUserAuthentication$0.call(Unknown Source)
    at org.hidetake.groovy.ssh.connection.ConnectionManager.configureUserAuthentication(ConnectionManager.groovy)
    at org.hidetake.groovy.ssh.connection.UserAuthentication$configureUserAuthentication$0.callCurrent(Unknown Source)
    at org.hidetake.groovy.ssh.connection.ConnectionManager.connectInternal(ConnectionManager.groovy:104)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
    at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
    at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:384)
    at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
    at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:69)
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:190)
    at org.hidetake.groovy.ssh.connection.ConnectionManager$_connectInternal_closure1.doCall(ConnectionManager.groovy:85)
    at org.hidetake.groovy.ssh.connection.ConnectionManager$_connectInternal_closure1.doCall(ConnectionManager.groovy)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
    at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
    at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:294)
    at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
    at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:42)
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:117)
    at org.hidetake.groovy.ssh.util.Utility.retry(Utility.groovy:52)
    at org.hidetake.groovy.ssh.util.Utility$retry.callStatic(Unknown Source)
    at org.hidetake.groovy.ssh.connection.ConnectionManager.connectInternal(ConnectionManager.groovy:83)
    at org.hidetake.groovy.ssh.connection.ConnectionManager.connectInternal(ConnectionManager.groovy)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite$PogoCachedMethodSiteNoUnwrapNoCoerce.invoke(PogoMetaMethodSite.java:210)
    at org.codehaus.groovy.runtime.callsite.PogoMetaMethodSite.callCurrent(PogoMetaMethodSite.java:59)
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:166)
    at org.hidetake.groovy.ssh.connection.ConnectionManager.connect(ConnectionManager.groovy:59)
    at org.hidetake.groovy.ssh.connection.ConnectionManager$connect.call(Unknown Source)
    at org.hidetake.groovy.ssh.session.SessionTask.wetRun(SessionTask.groovy:61)
    at org.hidetake.groovy.ssh.session.SessionTask.call(SessionTask.groovy:48)
    at java_util_concurrent_Callable$call$0.call(Unknown Source)
    at org.hidetake.groovy.ssh.core.Service.run(Service.groovy:81)
    at org.hidetake.groovy.ssh.core.Service$run$0.call(Unknown Source)
    at org.jenkinsci.plugins.sshsteps.SSHService.executeCommand(SSHService.groovy:177)
    at org.jenkinsci.plugins.sshsteps.steps.CommandStep$Execution$CommandCallable.execute(CommandStep.java:84)
    at org.jenkinsci.plugins.sshsteps.util.SSHMasterToSlaveCallable.call(SSHMasterToSlaveCallable.java:32)
    at hudson.remoting.LocalChannel.call(LocalChannel.java:45)
    at org.jenkinsci.plugins.sshsteps.steps.CommandStep$Execution.run(CommandStep.java:72)
    at org.jenkinsci.plugins.sshsteps.util.SSHStepExecution.lambda$start$0(SSHStepExecution.java:84)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

I've already read this post where the issue was caused by an unsupported key format. But I'm already using the older format with the -PEM flag on key creation.

What is wrong with this pipeline?