[JENKINS-58743] Allow to provide a custom path for master key

[Vlatombe]

See JENKINS-58743.

The following system properties can be used to control the behaviour

• jenkins.security.DefaultConfidentialStore.file allows to provide an alternative path to load/store the master key (when unset, defaults to $JENKINS_HOME/secrets/master.key as previously)
• jenkins.security.DefaultConfidentialStore.readOnly when true, prevents Jenkins from generating a master key. If the master key file doesn't exist, Jenkins fails to start.

User-facing doc jenkins-infra/jenkins.io#7859

Testing done

Create master.key beforehand in standard path

export JENKINS_HOME=/tmp/cc
mkdir -p $JENKINS_HOME/secrets
openssl rand -hex 128 >$JENKINS_HOME/secrets/master.key
java -Djenkins.master.key.readOnly=true -jar war/target/jenkins.war

✅ Normal startup sequence

Content of $JENKINS_HOME/secrets after startup

initialAdminPassword  jenkins.model.Jenkins.crumbSalt  master.key

Create master.key beforehand in custom path

export JENKINS_HOME=/tmp/cc
masterkey=$(mktemp)
openssl rand -hex 128 >$masterkey
java -Djenkins.master.key.readOnly=true -Djenkins.master.key.file=$masterkey -jar war/target/jenkins.war

✅ Normal startup sequence

Content of $JENKINS_HOME/secrets after startup

initialAdminPassword  jenkins.model.Jenkins.crumbSalt

Readonly missing master key

Starting with -Djenkins.master.key.readOnly=true and missing master.key.

Jenkins fails to start

[...]
2025-02-05 11:28:05.541+0000 [id=40]    INFO    hudson.lifecycle.Lifecycle#onStatusUpdate: Jenkins stopped
Exception in thread "Jenkins initialization thread" java.lang.Error: java.io.IOException: /tmp/cc/secrets/master.key does not exist and system property jenkins.security.DefaultConfidentialStore.readOnly is set. You must provide a valid master key file.
        at jenkins.security.ConfidentialStore.get(ConfidentialStore.java:93)
        at jenkins.model.Jenkins.<init>(Jenkins.java:977)
        at hudson.model.Hudson.<init>(Hudson.java:102)
        at hudson.model.Hudson.<init>(Hudson.java:87)
        at hudson.WebAppMain$3.run(WebAppMain.java:249)
Caused by: java.io.IOException: /tmp/cc/secrets/master.key does not exist and system property jenkins.security.DefaultConfidentialStore.readOnly is set. You must provide a valid master key file.
        at jenkins.security.DefaultConfidentialStore.<init>(DefaultConfidentialStore.java:85)
        at jenkins.security.DefaultConfidentialStore.<init>(DefaultConfidentialStore.java:71)
        at jenkins.security.DefaultConfidentialStore.<init>(DefaultConfidentialStore.java:67)
        at jenkins.security.ConfidentialStore.get(ConfidentialStore.java:90)
        ... 4 more

Proposed changelog entries

• Allow the master key to be stored in a separate location.

Proposed upgrade guidelines

N/A

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[jglick]

Jenkins doesn't fail to load

Insert a call to ConfidentialStore.get into the startup sequence somewhere?

[jglick]

BTW I think this comment has been obsolete for years?

[Vlatombe]

Still

jenkins/core/src/main/java/hudson/Util.java

Line 704 in 2c92eae

// Due to the stupid US export restriction JDK only ships 128bit version.

[timja]

Since Java 9 not true? https://stackoverflow.com/a/46857694/4951015

[Vlatombe]

Indeed, though would take non-trivial changes to migrate to the new key length. Not in scope of my current change.

[timja]

/label ready-for-merge

---

This PR is now ready for merge, after ~24 hours, we will merge it if there's no negative feedback.

Thanks!

[daniel-beck]

Please file a pull request to document these system properties at https://www.jenkins.io/doc/book/managing/system-properties/

[Vlatombe]

Filed jenkins-infra/jenkins.io#7859