@@ -237,7 +237,7 @@ $config = [
 ];
 ```
 
-## Auth Proc filters (OIDC)
+## Authentication Processing filters (OIDC)
 
 Standard SAML Auth Proc Filters do not run during OIDC authN because not
 all SAML entities are present (like a Service Provider). Instead, use the
@@ -277,6 +277,58 @@ $config = [
 ];
 ```
 
+### Per-client Auth Proc filters
+
+In addition to the global filters above, you can configure Auth Proc filters
+for a **specific client (Relying Party)**. This mimics the way SAML allows
+filters to be defined in Service Provider metadata.
+
+Client filters are stored together with the client in the database (as part of
+the client's extra metadata) and are managed from the client administration UI:
+
+- OIDC > Client Registry > (edit a client) > **Authentication Processing Filters**
+
+The value is entered as a JSON object using the same structure as the global
+`authproc.oidc` option (keyed by priority; each entry is a class string or an
+object with a `class` property), for example:
+
+```json
+{
+    "60": {
+        "class": "core:AttributeAdd",
+        "groups": ["members"]
+    }
+}
+```
+
+During authentication for that client, its filters are merged with the global
+filters by priority (the global filters run as the "IdP-side" list and the
+client filters as the "SP-side" list), exactly as SAML merges IdP and SP
+`authproc` filters.
+
+> **Security note:** Auth Proc filters name a PHP class that is instantiated and
+> executed on the OP during authentication. For this reason, per-client filters
+> can only be set by a trusted administrator through the admin UI / API. They are
+> **deliberately never accepted from client-supplied registration metadata**
+> (OIDC Dynamic Client Registration or OpenID Federation registration); any such
+> value present in registration metadata is ignored. This deny-list of
+> administrator-only client properties is defined in
+> `\SimpleSAML\Module\oidc\Entities\ClientEntity::ADMIN_ONLY_METADATA_KEYS` and
+> enforced in `ClientEntityFactory::fromRegistrationData()`.
+
+Alternatively, if you only need a global filter to run for selected clients, you
+can keep using the global `authproc.oidc` option together with a
+[preconditional filter](https://simplesamlphp.org/docs/stable/simplesamlphp-authproc.html#preconditional-filters),
+inspecting the client ID via `$state['Destination']['entityid']`:
+
+```php
+50 => [
+    'class' => 'core:AttributeAdd',
+    'groups' => ['members'],
+    '%precondition' => 'return $state["Destination"]["entityid"] === "https://rp.example.org/";',
+],
+```
+
 ## Client registration permissions
 
 You can allow users to register their own clients. Control this via the
 
@@ -61,6 +61,19 @@ in the OP discovery metadata via the `response_modes_supported` claim.
   (`query`, `fragment`, `form_post`) are allowed, so existing clients are
   unaffected. It can be narrowed, for example to `form_post` only, to protect
   against browser-swapping attacks (if supported by the client).
+- Authentication Processing Filters can now be configured per client (Relying
+Party), in addition to the global filters defined under `authproc.oidc`. This
+mimics defining authproc filters in SAML Service Provider metadata. During
+authentication the global (IdP-side) and per-client (SP-side) filters are merged
+by priority. The filters are stored together with the client (inside its extra
+metadata) and are managed from the client administration UI as a JSON object,
+using the same structure as the global filters. For security reasons, per-client
+filters can only be set by an administrator (via the admin UI / API) and are
+deliberately never accepted from client-supplied dynamic / OpenID Federation
+registration metadata (a filter names a PHP class executed on the OP, so
+honoring it from registration would be a remote code execution vector).
+  - Clients can now be configured with a new property related to the above:
+    - Authentication Processing Filters (`authproc`)
 - The encryption key (used to encrypt / decrypt artifacts like authorization
 codes and refresh tokens) can now optionally be set to a strong, pre-generated
 `\Defuse\Crypto\Key`, instead of always deriving it from the SimpleSAMLphp
 
@@ -370,6 +370,15 @@ protected function buildClientEntityFromFormData(
         $data[ClientEntity::KEY_ALLOWED_RESPONSE_MODES] : [];
         $extraMetadata[ClientEntity::KEY_ALLOWED_RESPONSE_MODES] = $allowedResponseModes;
 
+        // Per-client authproc filters. These are administrator-only (settable
+        // here, via the admin UI), and are deliberately never accepted from
+        // client-supplied registration metadata. See
+        // ClientEntityFactory::fromRegistrationData() and
+        // ClientEntity::ADMIN_ONLY_METADATA_KEYS.
+        $authProcFilters = is_array($data[ClientEntity::KEY_AUTH_PROC_FILTERS] ?? null) ?
+        $data[ClientEntity::KEY_AUTH_PROC_FILTERS] : [];
+        $extraMetadata[ClientEntity::KEY_AUTH_PROC_FILTERS] = $authProcFilters;
+
         return $this->clientEntityFactory->fromData(
             $identifier,
             $secret,
 
@@ -56,6 +56,26 @@ class ClientEntity implements ClientEntityInterface
     public const string KEY_IS_GENERIC = 'is_generic';
     public const string KEY_EXTRA_METADATA = 'extra_metadata';
     public const string KEY_ALLOWED_RESPONSE_MODES = 'allowed_response_modes';
+    /**
+     * Per-client Authentication Processing Filters. Stored as an entry inside
+     * the extra metadata JSON blob.
+     */
+    public const string KEY_AUTH_PROC_FILTERS = 'authproc';
+
+    /**
+     * Client properties (metadata keys) which are "administrator-only":
+     * they may only be set by a trusted administrator (via the admin UI / API,
+     * i.e. ClientEntityFactory::fromData()), and MUST NOT be honored when they
+     * arrive in client-supplied registration metadata (OIDC Dynamic Client
+     * Registration or OpenID Federation). See the deny-list handling and the
+     * accompanying explanation in
+     * \SimpleSAML\Module\oidc\Factories\Entities\ClientEntityFactory::fromRegistrationData().
+     *
+     * @var string[]
+     */
+    public const array ADMIN_ONLY_METADATA_KEYS = [
+        self::KEY_AUTH_PROC_FILTERS,
+    ];
 
 
     private string $secret;
@@ -236,6 +256,7 @@ public function toArray(): array
             ClaimsEnum::RequirePushedAuthorizationRequests->value => $this->getRequirePushedAuthorizationRequests(),
             ClaimsEnum::RequireSignedRequestObject->value => $this->getRequireSignedRequestObject(),
             ClaimsEnum::RequestUris->value => $this->getRequestUris(),
+            self::KEY_AUTH_PROC_FILTERS => $this->getAuthProcFilters(),
         ];
     }
 
@@ -429,6 +450,25 @@ public function getRequireSignedRequestObject(): bool
         return (bool)($this->extraMetadata[ClaimsEnum::RequireSignedRequestObject->value] ?? false);
     }
 
+    /**
+     * Per-client Authentication Processing Filters, in the same format as the
+     * global ModuleConfig::OPTION_AUTH_PROCESSING_FILTERS option. These run, in
+     * addition to the global filters, during authentication for this client
+     * (the SimpleSAMLphp ProcessingChain merges them as the "SP" side filters).
+     *
+     * @return array
+     */
+    public function getAuthProcFilters(): array
+    {
+        if (!is_array($this->extraMetadata)) {
+            return [];
+        }
+
+        $authProcFilters = $this->extraMetadata[self::KEY_AUTH_PROC_FILTERS] ?? null;
+
+        return is_array($authProcFilters) ? $authProcFilters : [];
+    }
+
     /**
      * @return string[]
      */
 
@@ -89,4 +89,9 @@ public function getRequireSignedRequestObject(): bool;
      * @return string[]
      */
     public function getRequestUris(): array;
+
+    /**
+     * @return array
+     */
+    public function getAuthProcFilters(): array;
 }
@@ -106,6 +106,32 @@ public function fromRegistrationData(
         ?string $clientIdentifier = null,
         ?array $federationJwks = null,
     ): ClientEntityInterface {
+        // Security: scrub administrator-only properties from client-supplied
+        // registration metadata.
+        //
+        // This method builds clients from metadata provided by a remote party,
+        // i.e. through OIDC Dynamic Client Registration (RFC 7591) or OpenID
+        // Federation (explicit / automatic) registration. Some client properties
+        // must never be controllable by the registering party, because honoring
+        // them would let an untrusted client influence server-side behavior. The
+        // prime example is `authproc` (per-client Authentication Processing
+        // Filters): a filter entry names a PHP class that is instantiated and
+        // executed on the OP during authentication, so accepting it from
+        // registration metadata would be a remote code execution vector.
+        //
+        // Such properties are settable ONLY by a trusted administrator, via the
+        // admin UI / API (ClientEntityFactory::fromData()). We strip every
+        // deny-listed key from the incoming metadata here, so it can neither be
+        // read below nor leak into a future code path. Any value an administrator
+        // has already set on an existing client is preserved because it is
+        // carried over from $existingClient->getExtraMetadata() further down (it
+        // does not come from $metadata).
+        //
+        // The deny-list itself lives next to the property definitions, in
+        // ClientEntity::ADMIN_ONLY_METADATA_KEYS.
+        foreach (ClientEntity::ADMIN_ONLY_METADATA_KEYS as $adminOnlyMetadataKey) {
+            unset($metadata[$adminOnlyMetadataKey]);
+        }
 
         $id = $clientIdentifier ?? $existingClient?->getIdentifier() ??
         $this->sspBridge->utils()->random()->generateID();
 
@@ -12,28 +12,29 @@
 namespace SimpleSAML\Module\oidc\Factories;
 
 use SimpleSAML\Auth\ProcessingChain;
-use SimpleSAML\Module\oidc\ModuleConfig;
 
 class ProcessingChainFactory
 {
-    public function __construct(
-        private readonly ModuleConfig $moduleConfig,
-    ) {
-    }
-
     /**
      * @codeCoverageIgnore
      * @throws \Exception
      */
     public function build(array $state): ProcessingChain
     {
+        // The IdP- and SP-side metadata (entityid + authproc filter lists) is
+        // the single source of truth prepared in
+        // AuthenticationService::runAuthProcs() and stored in the state.
+        // Here we only consume it;
+        // The IdP side carries the global authproc filters, the SP side the
+        // per-client ones, and the SimpleSAMLphp ProcessingChain merges them
+        // by priority.
         $idpMetadata = [
             'entityid' => $state['Source']['entityid'] ?? '',
-            // ProcessChain needs to know the list of authproc filters we defined in module_oidc configuration
-            'authproc' => $this->moduleConfig->getAuthProcFilters(),
+            'authproc' => $state['Source']['authproc'] ?? [],
         ];
         $spMetadata = [
             'entityid' => $state['Destination']['entityid'] ?? '',
+            'authproc' => $state['Destination']['authproc'] ?? [],
         ];
 
         return new ProcessingChain(
 
@@ -202,6 +202,71 @@ public function validateRequestUris(Form $form): void
         }
     }
 
+    /**
+     * Validate the per-client Authentication Processing Filters. The value is
+     * expected to be a JSON object/array in the same shape as the global
+     * ModuleConfig::OPTION_AUTH_PROCESSING_FILTERS option, i.e. a list keyed by
+     * priority where each filter is either a class string or an array with a
+     * 'class' key. JSON syntax itself is validated in getValues().
+     *
+     * @throws \Exception
+     */
+    public function validateAuthProcFilters(Form $form): void
+    {
+        $values = $form->getValues(self::TYPE_ARRAY);
+
+        $authProcFilters = $values[ClientEntity::KEY_AUTH_PROC_FILTERS] ?? [];
+
+        if (!is_array($authProcFilters)) {
+            $this->addError('Authentication Processing Filters must be a JSON object.');
+            return;
+        }
+
+        /**
+         * @var mixed $filter
+         */
+        foreach ($authProcFilters as $filter) {
+            if (is_string($filter)) {
+                continue;
+            }
+
+            if (!is_array($filter)) {
+                $this->addError(
+                    'Each Authentication Processing Filter must be a class string or an object: ' .
+                    var_export($filter, true),
+                );
+                continue;
+            }
+
+            if (!isset($filter['class']) || !is_string($filter['class'])) {
+                $this->addError(
+                    "Each Authentication Processing Filter object must have a string 'class' property: " .
+                    var_export($filter, true),
+                );
+            }
+        }
+    }
+
+    /**
+     * Cast integer-like string array keys to int, leaving all other keys (and
+     * the values) untouched. Only the top level is processed, which is where
+     * authproc filter priority keys live. Used to normalize priorities coming
+     * from the JSON-encoded authproc filters field.
+     */
+    protected function castNumericKeysToInt(array $array): array
+    {
+        $result = [];
+        /** @var mixed $value */
+        foreach ($array as $key => $value) {
+            if (is_string($key) && preg_match('/^-?\d+$/', $key) === 1) {
+                $key = (int) $key;
+            }
+            $result[$key] = $value;
+        }
+
+        return $result;
+    }
+
     public function validateJwks(mixed $jwks): void
     {
         if (is_null($jwks)) {
@@ -319,6 +384,24 @@ public function getValues(string|object|bool|null $returnType = null, ?array $co
             array_keys($this->getAllowedResponseModesValues()),
         );
 
+        $authProcFilters = trim((string)($values[ClientEntity::KEY_AUTH_PROC_FILTERS] ?? ''));
+        try {
+            /** @psalm-suppress MixedAssignment */
+            $decodedAuthProcFilters = $authProcFilters === '' ?
+            [] :
+            json_decode($authProcFilters, true, 512, JSON_THROW_ON_ERROR);
+            // Normalize numeric priority keys to integers. PHP already casts
+            // canonical integer string keys (e.g. "60") to int, but not forms
+            // like "08", so we make the priority type predictable for the
+            // SimpleSAMLphp ProcessingChain.
+            $values[ClientEntity::KEY_AUTH_PROC_FILTERS] = is_array($decodedAuthProcFilters) ?
+            $this->castNumericKeysToInt($decodedAuthProcFilters) :
+            $decodedAuthProcFilters;
+        } catch (\JsonException $e) {
+            $this->addError('Authentication Processing Filters JSON error: ' . $e->getMessage());
+            $values[ClientEntity::KEY_AUTH_PROC_FILTERS] = [];
+        }
+
         return $values;
     }
 
@@ -390,6 +473,11 @@ public function setDefaults(object|array $values, bool $erase = false): static
             $values[ClientEntity::KEY_ALLOWED_RESPONSE_MODES],
         ) ? $values[ClientEntity::KEY_ALLOWED_RESPONSE_MODES] : [];
 
+        $authProcFilters = $values[ClientEntity::KEY_AUTH_PROC_FILTERS] ?? null;
+        $values[ClientEntity::KEY_AUTH_PROC_FILTERS] = (is_array($authProcFilters) && $authProcFilters !== []) ?
+        (string)json_encode($authProcFilters, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES) :
+        '';
+
         parent::setDefaults($values, $erase);
 
         return $this;
@@ -413,6 +501,7 @@ protected function buildForm(): void
         $this->onValidate[] = $this->validateProtocolJwks(...);
         $this->onValidate[] = $this->validateJwksUri(...);
         $this->onValidate[] = $this->validateRequestUris(...);
+        $this->onValidate[] = $this->validateAuthProcFilters(...);
 
         $this->setMethod('POST');
         $this->addComponent($this->csrfProtection, Form::ProtectorId);
@@ -494,6 +583,13 @@ protected function buildForm(): void
         $this->addCheckbox(ClaimsEnum::RequireSignedRequestObject->value, 'Require Signed Request Object');
         $this->addTextArea(ClaimsEnum::RequestUris->value, 'Request URIs (OIDC Core / JAR, one per line)', null, 5)
             ->setHtmlAttribute('class', 'full-width');
+
+        $this->addTextArea(
+            ClientEntity::KEY_AUTH_PROC_FILTERS,
+            Translate::noop('Authentication Processing Filters'),
+            null,
+            5,
+        )->setHtmlAttribute('class', 'full-width');
     }
 
     /**