import org.apache.jackrabbit.oak.spi.security.user.util.PasswordUtil
import org.apache.jackrabbit.oak.spi.commit.CommitInfo
import org.apache.jackrabbit.oak.spi.commit.EmptyHook

class Global {
    static adminNode = null;
}

void findAdminNode(ub) {
    if (ub.hasProperty("rep:principalName")) {
        if ("rep:principalName = admin".equals(ub.getProperty("rep:principalName").toString())) {
            Global.adminNode = ub;
        }
    }
    ub.childNodeNames.each { it -> 
        if (Global.adminNode == null) {
            findAdminNode(ub.getChildNode(it));
        }
    }
}

ub = session.store.root.builder();
findAdminNode(ub.getChildNode("home").getChildNode("users"));

if (Global.adminNode) {
    println("Found admin node: " + Global.adminNode.toString());
    Global.adminNode.setProperty("rep:password", PasswordUtil.buildPasswordHash("admin"));
    session.store.merge(ub, EmptyHook.INSTANCE, CommitInfo.EMPTY);
} else {
    println("Could not find admin node.");
}