This program prints the Microsoft JSON Web Key Set (JWKS) certificate and public keys. Also demonstrated is two methods to create a public key from the information provided by the JWKS data. For details see my article on Azure Open ID Connect JSON Web Key Set - http://www.jhanley.com/azure-openid-connect-json-web-key-set

composer.json

{
    "require": {
        "phpseclib/phpseclib": "^2.0",
    }
}

print_jwks_public_keys_2.php

<?php
/*****************************************************************************
* Date Created: 2021-09-30
* Last Update:  2021-09-30
* https://www.jhanley.com - Google Cloud
* Copyright (c) 2021, John J. Hanley
* Author: John J. Hanley
* License: MIT
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*****************************************************************************/

/*
 * This program prints the Microsoft JSON Web Key Set (JWKS) certificate and
 * public keys. Also demonstrated is two methods to create a public key from
 * the information provided by the JWKS data.
*/

declare(strict_types = 1);
require 'vendor/autoload.php';

use phpseclib\Crypt\RSA;

$openid_configuration_uri = 'https://login.microsoftonline.com/common/v2.0/.well-known/openid-configuration';
$microsoft_jwks_uri = '';

function custom_file_get_contents($path, &$error_msg)
{
	/*
	 * This is a custom wrapper for file_get_contents.
	 * The purpose is to catch errors in a string and return
	 * the error message to the calling function.
	*/

	$error_msg = "";

	$contents = @file_get_contents($path);

	if (empty($contents))
	{
		$msg = error_get_last()['message'];
		$error = explode(': ', $msg);
		$error_msg = trim($error[count($error) - 1]);
		return "";
	}

	return strval($contents);
}

function load_openid_configuration()
{
	/*
	 * Load the Microsoft OpenID Connect Metadata Document.
	*/

	global $openid_configuration_uri;
	global $microsoft_jwks_uri;

	echo 'loading: ' . $openid_configuration_uri . PHP_EOL;

	$content = custom_file_get_contents($openid_configuration_uri, $error_msg);

	if (empty($content))
	{
		echo "Error: Cannot read configuration from $openid_configuration_uri" . PHP_EOL;
		echo "Message: $error_msg" . PHP_EOL;

		return 1;
	}

	$config = json_decode($content, true);

	$microsoft_jwks_uri = $config['jwks_uri'];

	# echo $microsoft_jwks_uri . PHP_EOL;

	return 0;
}

function get_public_key($key)
{
	/*
	 * Create a public key from Modulus and Exponent.
	*/

	# echo PHP_EOL;
	# echo 'N: ' . $key['n'] . PHP_EOL;
	# echo 'E: ' . $key['e'] . PHP_EOL;

	$n = $key['n'];		# Modulus
	$e = $key['e'];		# Exponent

	$n = strtr($n, '-_', '+/');

	$rsa = new RSA();

	$key = "<RSAKeyPair>"
		. "<Modulus>" . $n . "</Modulus>"
		. "<Exponent>" . $e . "</Exponent>"
		. "</RSAKeyPair>";

	$rsa->loadKey($key, RSA::PUBLIC_FORMAT_XML);

	# echo $rsa . PHP_EOL;

	# CRYPT_RSA_PUBLIC_FORMAT_PKCS1
	return $rsa;
}

function make_certificate($key)
{
	/*
	 * Create a certificate from the x5c value
	*/

	$cert = "-----BEGIN CERTIFICATE-----\n";
	$cert .= $key['x5c'][0] . "\n";
	$cert .= "-----END CERTIFICATE-----";

	return $cert;
}

function get_public_key_from_cert($cert)
{
	/*
	 * Extract the public key from a certificate.
	*/

	$pub_key = openssl_pkey_get_public($cert);
	$keyData = openssl_pkey_get_details($pub_key);

	return $keyData['key'];
}

function print_public_certificates()
{
	/*
	 * Load the Microsoft JSON Web Key Set and print the certificate and
	 * public key for each Key ID. This function prints the public key twice.
	 * This function demonstrates how to create a public key from the Modulus
	 * and Exponent, and from a certificate.
	*/

	global $microsoft_jwks_uri;

	echo 'loading public certificates from ' . $microsoft_jwks_uri . PHP_EOL;

	$content = custom_file_get_contents($microsoft_jwks_uri, $error_msg);

	if (empty($content))
	{
		echo "Error: Cannot read configuration from $microsoft_jwks_uri" . PHP_EOL;
		echo "Message: $error_msg" . PHP_EOL;

		return;
	}

	$config = json_decode($content, true);

	foreach($config as $keys)
	{
		foreach($keys as $key)
		{
			echo PHP_EOL;
			echo "Key ID: " . $key['kid'] . PHP_EOL;

			$cert = make_certificate($key);

			echo "Certificate" . PHP_EOL;
			echo $cert . PHP_EOL;

			echo "Public Key from cert:" . PHP_EOL;
			echo get_public_key_from_cert($cert) . PHP_EOL;

			echo "Public Key from m,e:" . PHP_EOL;
			echo get_public_key($key) . PHP_EOL;
		}
	}
}

# Load the OpenID Connect Metadata Document
$ret = load_openid_configuration();

if ($ret !== 0)
{
	exit(1);
}

print_public_certificates();