PHP how to access "value" of JSON object which has no "name" in foreach loop

I’ve got a set of "objects", each of which has an ID, and couple or properties. I want to store this in JSON format in a file. In the application, I first need to show a list of all "objects" with its properties. Secondly, I need to access one entry by its ID and only work with those properties.

The JSON file looks like this:

{
    "ID-001": {
        "Tag1": "value1a",
        "Tag2": "value1b"
    },
        
    "ID-002": {
        "Tag1": "value2a",
        "Tag2": "value2b"
    },
        
    "ID-003": {
        "Tag1": "value3a",
        "Tag2": "value3b"
    }
}

In this sample PHP code, I know how to work with properties, given I already have the onject’s ID, and I can list a specific property for all objects.

<?php

$objects = json_decode(file_get_contents("sample.json", TRUE), FALSE); 

var_dump($objects) ."n";
print "-----------------------------------------n";

$ix = "ID-001";

if (!isset($objects->$ix)) {
    print "Key {$ix} does not exist." . "n";
} else {
    print "Tag1 has value: {$objects->$ix->Tag1}n";
}

$ix = "ID-004";

if (!isset($objects->$ix)) {
    print "Key {$ix} does not exist." . "n";
} else {
    print "Tag1 has value: {$objects->$ix->Tag1}n";
}

print "-----------------------------------------n";

foreach ($objects as $object) {
    print "Tag1 has value: {$object->Tag1}n";
}

?>

What I can’t seem to find out, is how I can access the ID of the objects in a loop, so get a list of IDs. Can I?