chore: add php-cs-fixer with PSR-12 config and CI check

- Add friendsofphp/php-cs-fixer to require-dev
- Create .php-cs-fixer.dist.php configured for @PSR12 ruleset
- Add php-cs-fixer dry-run step to CI pipeline
- Auto-fix existing PSR-12 violations
- Document code style tooling in readme.md

src/Data/Payload.php

@@ -1,4 +1,5 @@
 <?php
+
 declare(strict_types=1);
 
 namespace App\Data;
@@ -7,14 +8,16 @@ use App\Enum\Scope;
 use Symfony\Component\HttpFoundation\InputBag;
 
 /** when scope is IP but ip-access is disabled, scope is to be considered cookie */
-final class Payload {
+final class Payload
+{
     public string $id;    /* session name, identifying who is logging in */
     public string $token; /* TOTP, typically six digits */
     public string $nonce; /* random unique string, to block duplicate submissions */
     public bool   $json;  /* should we return json (for the login page) */
     public Scope  $scope; /* type of access being requested */
 
-    public static function decode(string $base64url): ?Payload {
+    public static function decode(string $base64url): ?Payload
+    {
         /* convert the base64url into json string */
         $base64 = strtr($base64url, '-_', '+/');
         $base64 .= str_repeat('=', (4 - strlen($base64) % 4) % 4);
@@ -29,7 +32,8 @@ final class Payload {
         return null;
     }
 
-    public static function load(InputBag $input): ?Payload {
+    public static function load(InputBag $input): ?Payload
+    {
         /* convert form data into real data */
         if ($input->has('username') && $input->has('nonce') && $input->has('totp')) {
             return Payload::create((object)[
@@ -42,7 +46,8 @@ final class Payload {
         return null;
     }
 
-    public static function create(object $data): ?Payload {
+    public static function create(object $data): ?Payload
+    {
         /* if missing required fields id, nonce, or token */
         if (strlen(trim($data->id    ?? '')) < 1 ||
             strlen(trim($data->nonce ?? '')) < 1 ||
@@ -63,11 +68,13 @@ final class Payload {
         return Payload::constrict($payload);
     }
 
-    public function toString(): string {
+    public function toString(): string
+    {
         return json_encode($this);
     }
 
-    private static function constrict(Payload $payload): Payload {
+    private static function constrict(Payload $payload): Payload
+    {
         /* When scope is None, json will be considered false. */
         if ($payload->scope === Scope::None) {
             $payload->json = false;