FIX TOTP issuer and label are now extensible (#38)

FIX TOTP issuer and label are now extensible

README.md

@@ -74,6 +74,23 @@ SilverStripe\TOTP\RegisterHandler:
   user_help_link: 'https://intranet.mycompany.com/help-docs/using-totp'
 ```
 
+### TOTP issuer and label
+
+The TOTP "issuer" is the SilverStripe site name (set in SiteConfig) by default, and the "label" is the member's email
+address by default. These are the values that show up in your authenticator app. You can change these if you need
+to use something else, by writing an extension on `RegisterHandler`:
+
+```php
+class MyTOTPRegisterHandlerExtension extends Extension
+{
+    public function updateTotp(\OTPHP\TOTPInterface $totp, \SilverStripe\Security\Member $member)
+    {
+        $totp->setLabel($member->getCustomTOTPLabel());
+        $totp->setIssuer('My web project');
+    }
+}
+```
+
 ## License
 
 See [License](LICENSE.md)

src/RegisterHandler.php

@@ -6,6 +6,7 @@
 use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Core\Config\Configurable;
 use SilverStripe\Core\Environment;
+use SilverStripe\Core\Extensible;
 use SilverStripe\Core\Injector\Injector;
 use SilverStripe\MFA\Exception\AuthenticationFailedException;
 use SilverStripe\MFA\Method\Handler\RegisterHandlerInterface;
@@ -21,6 +22,7 @@
 class RegisterHandler implements RegisterHandlerInterface
 {
     use Configurable;
+    use Extensible;
     use TOTPAware;
 
     /**
@@ -54,6 +56,8 @@ public function start(StoreInterface $store): array
         }
         $totp->setIssuer(SiteConfig::current_site_config()->Title);
 
+        $this->extend('updateTotp', $totp, $member);
+
         return [
             'enabled' => !empty(Environment::getEnv('SS_MFA_SECRET_KEY')),
             'uri' => $totp->getProvisioningUri(),