Fixed OIDC handling when no JWKS 'use' prop exists

Now assume, based on OIDC discovery spec, that keys without 'use' are
'sig' keys. Should not affect existing use-cases since existance of such
keys would have throw exceptions in prev. versions of bookstack.

For #3869

app/Auth/Access/Oidc/OidcJwtSigningKey.php

@@ -67,11 +67,10 @@ class OidcJwtSigningKey
             throw new OidcInvalidKeyException("Only RS256 keys are currently supported. Found key using {$alg}");
         }
 
-        if (empty($jwk['use'])) {
-            throw new OidcInvalidKeyException('A "use" parameter on the provided key is expected');
-        }
-
-        if ($jwk['use'] !== 'sig') {
+        // 'use' is optional for a JWK but we assume 'sig' where no value exists since that's what
+        // the OIDC discovery spec infers since 'sig' MUST be set if encryption keys come into play.
+        $use = $jwk['use'] ?? 'sig';
+        if ($use !== 'sig') {
             throw new OidcInvalidKeyException("Only signature keys are currently supported. Found key for use {$jwk['use']}");
         }
 

app/Auth/Access/Oidc/OidcProviderSettings.php

@@ -15,40 +15,17 @@ use Psr\Http\Client\ClientInterface;
  */
 class OidcProviderSettings
 {
-    /**
-     * @var string
-     */
-    public $issuer;
-
-    /**
-     * @var string
-     */
-    public $clientId;
-
-    /**
-     * @var string
-     */
-    public $clientSecret;
-
-    /**
-     * @var string
-     */
-    public $redirectUri;
-
-    /**
-     * @var string
-     */
-    public $authorizationEndpoint;
-
-    /**
-     * @var string
-     */
-    public $tokenEndpoint;
+    public string $issuer;
+    public string $clientId;
+    public string $clientSecret;
+    public ?string $redirectUri;
+    public ?string $authorizationEndpoint;
+    public ?string $tokenEndpoint;
 
     /**
      * @var string[]|array[]
      */
-    public $keys = [];
+    public ?array $keys = [];
 
     public function __construct(array $settings)
     {
@@ -164,9 +141,10 @@ class OidcProviderSettings
     protected function filterKeys(array $keys): array
     {
         return array_filter($keys, function (array $key) {
-            $alg = $key['alg'] ?? null;
+            $alg = $key['alg'] ?? 'RS256';
+            $use = $key['use'] ?? 'sig';
 
-            return $key['kty'] === 'RSA' && $key['use'] === 'sig' && (is_null($alg) || $alg === 'RS256');
+            return $key['kty'] === 'RSA' && $use === 'sig' && $alg === 'RS256';
         });
     }
 

app/Auth/Access/Oidc/OidcService.php

@@ -52,7 +52,6 @@ class OidcService
     {
         $settings = $this->getProviderSettings();
         $provider = $this->getProvider($settings);
-
         return [
             'url'   => $provider->getAuthorizationUrl(),
             'state' => $provider->getState(),