Support PHP 7.2 and 7.3

As those are still supported and used by many Unix distributions.
Many software is running on PHP 7.2 and 7.3 and the code base should
support those versions.

.github/workflows/ci.yaml

@@ -14,6 +14,8 @@ jobs:
     strategy:
       matrix:
         php-version:
+          - 7.2
+          - 7.3
           - 7.4
     steps:
       - name: Checkout

composer.json

@@ -10,9 +10,9 @@
         }
     ],
     "require": {
-        "guzzlehttp/guzzle": "^6.5",
         "ext-json": "*",
-		"php": "^7.4"
+        "guzzlehttp/guzzle": "^6.5",
+        "php": "7.2.* || 7.3.* || 7.4.*"
     },
     "autoload": {
         "files": [ "src/Constants/VerificationTypes.php" ],

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "5ddae281cdc978a7b2312629a0fec326",
+    "content-hash": "b9cf8f698cb3698b7ded4c56e55e8421",
     "packages": [
         {
             "name": "guzzlehttp/guzzle",
@@ -2660,7 +2660,7 @@
     "prefer-lowest": false,
     "platform": {
         "ext-json": "*",
-        "php": "^7.4"
+        "php": "7.2.* || 7.3.* || 7.4.*"
     },
     "platform-dev": [],
     "plugin-api-version": "1.1.0"

src/Configuration/Settings.php

@@ -5,11 +5,30 @@ namespace SkillDisplay\PHPToolKit\Configuration;
 
 class Settings
 {
-    private string $user_secret;
-    private string $apiKey;
-    private int $verifierID;
-    private string $APIUrl;
-    private string $mySkillDisplayUrl;
+    /**
+     * @var string
+     */
+    private $user_secret = '';
+
+    /**
+     * @var string
+     */
+    private $apiKey = '';
+
+    /**
+     * @var int
+     */
+    private $verifierID = 0;
+
+    /**
+     * @var string
+     */
+    private $APIUrl = '';
+
+    /**
+     * @var string
+     */
+    private $mySkillDisplayUrl = '';
 
     public function getVerifierID(): int
     {

src/Verification/Issuer.php

@@ -9,8 +9,15 @@ use SkillDisplay\PHPToolKit\Configuration\Settings;
 
 class Issuer
 {
-    private Settings $settings;
-    private string $apislug = '/api/v1/verification/create';
+    /**
+     * @var Settings
+     */
+    private $settings;
+
+    /**
+     * @var string
+     */
+    private $apislug = '/api/v1/verification/create';
 
     /**
      * @param int $ID ID of the Skill or SkillSet
@@ -72,8 +79,7 @@ class Issuer
         string $useremail,
         string $vtype,
         bool $isSkillSet = false
-    ): ResponseInterface
-    {
+    ): ResponseInterface {
         $requestData = $this->generateSignedRequestData($skillID, $useremail, $vtype, $isSkillSet);
 
         $client = new \GuzzleHttp\Client();