[#3758] Add docs regarding the BRK validation plugin

docs/configuration/validation/brk.rst

@@ -0,0 +1,45 @@
+.. _configuration_validation_brk:
+
+=========================
+BRK - Zakelijk gerechtigd
+=========================
+
+The special *AddressNL* component has a specific validator available, that can
+check if the currently logged in user is the business owner of the filled-in property.
+
+Configuration
+=============
+
+1. Obtain a BRK API key.
+2. In Open Forms, navigate to: **Configuration** > **Services**.
+3. Click **Add service** and fill in the following details:
+
+   * **Label**: *Fill in a human readable label*, for example: ``Basisregistratie Kadaster (BRK)``
+   * **Type**: ORC (Overige).
+   * **API root URL**: *The API URL provided by KvK but typically:* ``https://api.brk.kadaster.nl/esd-eto-apikey/bevragen/v2/``.
+   * **Authorization type**: API key.
+   * **Header key**: ``X-Api-Key``.
+   * **Header value**: *The KvK API key obtained in step 1*.
+
+4. Click **Save**
+5. Navigate to **Configuration** > **Configuration overview**. In the **Validator plugins**
+   group, click on **Configuration** for the **Validation plugin config: BRK - Zakelijk gerechtigd** line.
+6. Select for the **BRK API**, the **Basisregistratie Kadaster (BRK)** option, that we just created in step 3.
+7. Click **Save**
+8. When building a form, add an *AddressNL* component from the *Special* group.
+9. In the **Validation** tab, select *BRK - Zakelijk gerechtigd*.
+
+.. note::
+
+   This validation plugin is only available if an :ref:`authentication plugin <configuration_authentication_index>`
+   that provides a BSN is being used.
+
+
+Technical
+=========
+
+=======  ==================
+API      Supported versions
+=======  ==================
+BRK API  2.0
+=======  ==================

docs/configuration/validation/index.rst

@@ -8,3 +8,4 @@ Validation plugins
    :maxdepth: 1
 
    kvk
+   brk