Add test to verify Argon2 works in PHP

This test verifies that Argon2 actually works for PHP images where it should.
This is to ensure that the Argon2 from Buster does not magically change to
become incompatible.

see: https://github.com/docker-library/php/pull/677#issuecomment-408546100

test/config.sh

@@ -143,6 +143,7 @@ imageTests+=(
 	[php]='
 		php-ext-install
 		php-hello-world
+		php-argon2
 	'
 	[php:apache]='
 		php-apache-hello-web

test/tests/php-argon2/container.php

@@ -0,0 +1,26 @@
+<?php
+$success = true;
+
+// Argon2 is supported for PHP >= 7.2 on Debian >= 9 or Alpine >= 3.8
+if (file_exists('/etc/alpine-release')) {
+	$baseImage = version_compare(file_get_contents('/etc/alpine-release'), '3.8.0') >= 0;
+}
+else if (file_exists('/etc/debian_version')) {
+	$baseImage = version_compare(file_get_contents('/etc/debian_version'), '9.0') >= 0;
+}
+else {
+	echo "Unknown base image\n";
+	$success = false;
+}
+
+if ($baseImage && version_compare(PHP_VERSION, '7.2.0') >= 0) {
+	if (!defined('PASSWORD_ARGON2I')) {
+		echo "constant PASSWORD_ARGON2I is not defined\n";
+		$success = false;
+	}
+	if (!password_verify('password', '$argon2i$v=19$m=8,t=1,p=1$RWxaRlZ0d1FTa3RSY1c1OQ$c7a/rJlPgvH9ItPi74UGuh0tdCBhpdDF7b/nA3QweX8')) {
+		echo "Failed check test vector\n";
+		$success = false;
+	}
+}
+var_dump($success);

test/tests/php-argon2/expected-std-out.txt

@@ -0,0 +1 @@
+bool(true)

test/tests/php-argon2/run.sh

@@ -0,0 +1 @@
+../run-php-in-container.sh