Kevin Burkholder

{eac}SoftwareRegistry Webhook Endpoints is an extension plugin to <a href="https://swregistry.earthasylum.com/software-registration-server/" rel="nofollow ugc">{eac}SoftwareRegistry Software Registration Server</a>.
WooCommerce Webhooks are used to create or update a software registration in {eac}SoftwareRegistry when a WooCommerce order is created or updated.
<blockquote>
A Webhook is an event notification sent to a URL of your choice. Users can configure them to trigger events on one site to invoke behavior on another.
</blockquote>
The Software Registration Webhooks use the same internal methods as the Software Registry API (see <a href="https://swregistry.earthasylum.com/software-registry-sdk/" rel="nofollow ugc">Implementing the Software Registry SDK</a>).
We use webhooks so that you may sell your software on a different site then where you register your software. When an order is created or updated on your WooCommerce site, that order information is sent to your registration server via a webhook so that the registration server may create or update the registration.
WooCommerce Webhooks are created by going to: WooCommerce → Settings → Advanced → Webhooks from the dashboard of your WooCommerce shop site.
To get to the settings for this extension, go to Software Registry → Settings → Woocommerce from the dashboard of your software registration server.
On your WooCommerce site, use the Webhook Secret and Order Delivery URL defined by this extension when creating your webhooks. The Webhook Secret is used to authenticate the webhook and the Delivery URL is the webhook end-point (your registration server).
You should create a WooCommerce Webhook for Order created and Order updated, and you may optionally create webhooks for Order deleted and Order restored if your want registrations to be terminated or reactivated when an order is moved to the trash or restored.
* See <a href="#subscriptions" rel="nofollow ugc">Subscriptions</a> below.
On your registration server, select the appropriate Webhook Endpoints in this extension based on the WooCommerce webhooks created.
<h4>Product Variations and Registry Values</h4>
On your shop site, you may create a variable product with a product attribute (‘Used for variations’ checked), like:
<pre><code>registry_license -> 'Lite' | 'Basic' | 'Standard' | 'Professional' | 'Enterprise' | 'Developer'
</code></pre>
— and/or —
<pre><code>registry_count -> '1-User' | '10-Users' | '50-Users' | '100-Users' | 'Unlimited Users'
</code></pre>
Then configure (or remove) each of the variations accordingly. 
This produces a product variation for each license level (or user count) and passes <code>registry_license</code> (or <code>registry_count</code>) through the webhook overriding the default registration server settings.
As well, you may create an attribute and variation like:
<pre><code>registry_expires -> '14 Days' | '30 Days' | '6 Months' | '1 Year'
</code></pre>
To override the default registration term.
These variations may be combined to create a large number of variable products, each passing the given registry values through the webhooks. For example, one variable product may have a variation combination of <code>'Basic', '10-users', '6 Months'</code>
<h4>Item Mapping</h4>
On your registration server, you may specify the items (SKUs) that are to be registered in the Registration Item Mapping as:
<pre><code>item_sku=package_name or `item_sku=package_name1,package_name2` (to create a bundle).
</code></pre>
Even if the item sku is the product to be registered, enter <code>item_sku=item_sku</code>.
Items that don’t match these SKU(s) will be ignored.
Since WooCommerce won’t allow duplicate SKUs, regular expressions may be used for “item_sku” matching. For example: <code>MyItemSku*=MyPackage</code> Will match any SKU in the order beginning with “MyItemSku” (e.g. “MyItemSku_1”, “MyItemSku_2”) and map (register) it as “MyPackage”.
<h4>Subscriptions</h4>
By adding <a href="https://swregistry.earthasylum.com/subscriptions-for-woocommerce/" rel="nofollow ugc">{eac}SoftwareRegistry Subscriptions for WooCommerce</a> to your WooCommerce store site, subscription orders and updates (when using <a href="https://woocommerce.com/document/subscriptions/" rel="nofollow ugc">Woo Subscriptions</a> or <a href="https://codecanyon.net/item/sumo-subscriptions-woocommerce-subscription-system/16486054" rel="nofollow ugc">SUMO Subscription</a>), as well as product meta data, may also be passed to your registration server.
{eac}SoftwareRegistry Subscriptions for WooCommerce is a plugin, installed on your WooCommerce site, that adds a custom Webhook topic for subscription updates to the WooCommerrce webhooks, and adds subscription and product data to WooCommerce order webhooks.
On your WooCommerce site, add a new Webhook using {eac}SoftwareRegistry WC Subscription or {eac}SoftwareRegistry Sumo Subscription for the topic; the same Webhook Secret used for the order webhooks; and the Subscription Delivery URL rather than the Order Delivery URL.
With this plugin enabled, not only can you update registrations by order updates, but also by subscription updates, including renewals, expirations, and cancelations, making it easy to keep your registrations in sync with your subscriptions.
In addition, this plugin will add product meta data to the orders and subscriptions passed through the webhooks so that you may define registry values as custom fields at the product level.
For example, rather than needing to create variable products, you can simply add custom fields:
<pre><code>registry_license -> 'Basic'
registry_count -> '10-Users'
registry_expires -> '6 Months'
</code></pre>
And, rather than relying on the <code>item_sku</code> list in the Registration Item Mapping, you can add a custom field…
<pre><code>registry_product -> 'package_name'
</code></pre>
…that will register or update any subscription for the given item as <code>package_name</code> regardless of the item’s SKU or the Registration Item Mapping list.
If all of your orders are subscriptions…
With this plugin enabled on your shop site, there’s a high probability you don’t need to use the “order” webhooks. Your subscriptions will be updated more efficiently from the shop subscription records.
When a new (or renewal) subscription order is created, it will trigger the “Order created”, “Order updated” (payment processed) and the “Subscription updated” webhooks when all you need is the subscription to create or update the registration.
On the other hand, since this plugin adds an array of subscription records to the orders passed through the webhooks, you may prefer to use only the order webhooks and not the subscription webhook.
<h4>Return Value</h4>
As of version 1.1, this plugin now returns a result array which can be retrieved via the <code>woocommerce_webhook_delivery</code> action:
<pre><code>array(
 'action' => string // the webhook action,
 'resource' => int // the webhook resource id (order/subscription id),
 'status' => string // 'success' | 'ignored' | 'error',
 'result' => array|string // success: array of [ sku => [status => registry_key | error_message] ]
 // ignored|error: string error_message
)
</code></pre>
Note that ‘success’ means the webhook was succesfull, ‘result’ could contain an error status/message from {eac}SoftwareRegistry.
Examples:
<pre><code>array(
 'action' => 'order.created',
 'resource' => 2715,
 'status' => 'ignored',
 'result' => 'order with subscription',
),

array(
 'action' => 'action.wc_eacswregistry_sumosub',
 'resource' => 2715,
 'status' => 'success',
 'result' => array (
 0 => array(
 'eacDoojigger' => array(
 '200' => 'bad53cd3-f397-4f47-9d28-xxxxxxxxxxxx',
 ),
 ),
 1 => array(
 'eacSoftwareRegistry' => array(
 '406' => 'registration with this email and product already exists',
 ),
 ),
 ),
),
</code></pre>
<h4>See Also</h4>
<ul>
<li>
<a href="https://swregistry.earthasylum.com/software-registration-server/" rel="nofollow ugc">{eac}SoftwareRegistry – Software Registration Server</a>
</li>
<li>
<a href="https://swregistry.earthasylum.com/subscriptions-for-woocommerce/" rel="nofollow ugc">{eac}SoftwareRegistry Subscriptions for WooCommerce</a>
</li>
<li>
<a href="https://swregistry.earthasylum.com/software-registry-sdk/" rel="nofollow ugc">Implementing the Software Registry SDK</a>
</li>
</ul>
<h3>Copyright</h3>
<h4>Copyright © 2019-2025, EarthAsylum Consulting, distributed under the terms of the GNU GPL.</h4>
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should receive a copy of the GNU General Public License along with this program. If not, see <a href="https://www.gnu.org/licenses/" rel="nofollow ugc">https://www.gnu.org/licenses/</a>.

{eac}SoftwareRegistry WooCommerce Webhook Endpoints

Enables the use of WooCommerce Webhooks to create or update a software registration in {eac}SoftwareRegistry when an order or subscription is created  …

{eac}SoftwareRegistry Distribution SDK is an extension plugin to <a href="https://swregistry.earthasylum.com/software-registration-server/" rel="nofollow ugc">{eac}SoftwareRegistry Software Registration Server</a>.
The Software Registry Distribution SDK is used to generate a custom PHP package that you can include in your software project to register your product with your registration server and manage that registration.
A custom version of this document is included in the generated SDK package.
The SDK provides most of the PHP code you will need to implement the Application Program Interface with your Software Registration Server.
Included with the Software Registration SDK package…
<ul>
<li><code>(your_productid)_registration.(wordpress_or_filebased).trait.php</code></li>
<li><code>(your_productid)_registration.includes.php</code></li>
<li><code>(your_productid)_registration.interface.php</code></li>
<li><code>(your_productid)_registration.interface.trait.php</code></li>
<li><code>(your_productid)_registration.refresh.php</code></li>
<li><code>(your_productid)_registration.readme.md</code></li>
</ul>
<h4>Software Registry Implementation</h4>
After extracting the <code>(your_productid)_registration.zip</code> file, move the <code>(your_productid)_registration</code> folder to your project.
In your project or class file, include <code>(your_productid)_registration/(your_productid)_registration.includes.php</code> to load the required interface and traits.
Your class file must then:
<ul>
<li>implement <code>\(your_namespace)\Interfaces\(your_productid)_registration</code></li>
<li>use <code>\(your_namespace)\Traits\(your_productid)_registration_(wordpress_or_filebased)</code></li>
</ul>
Example:
<pre><code>include "(your_productid)_registration/(your_productid)_registration.includes.php";

class <your_classname> implements \(your_namespace)\Interfaces\(your_productid)_registration
{
 use \(your_namespace)\Traits\(your_productid)_registration_(wordpress_or_filebased);
 ...
}
</code></pre>
(your_productid)_registration.interface.php will have your product and registration server API constants.
<pre><code>const SOFTWARE_REGISTRY_PRODUCTID = '{your_software_registry_productid}';
const SOFTWARE_REGISTRY_HOST_URL = '{your_software_registry_host_url}';
const SOFTWARE_REGISTRY_CREATE_KEY = '{your_software_registry_create_key}';
const SOFTWARE_REGISTRY_UPDATE_KEY = '{your_software_registry_update_key}';
const SOFTWARE_REGISTRY_READ_KEY = '{your_software_registry_read_key}';
</code></pre>
<h4>Using The API</h4>
API Parameters
API parameters are passed as an array:
<pre><code>$apiParams =
[
 'registry_key' => 'unique ID', // * registration key (assigned by registry server)
 'registry_name' => 'Firstname Lastname', // registrant's full name
 'registry_email' => 'email@domain.com', // * registrant's email address
 'registry_company' => 'Comapny/Organization Name', // registrant's company name
 'registry_address' => 'Street\n City St Zip', // registrant's full address (textarea)
 'registry_phone' => 'nnnnnnnnnn', // registrant's phone
 'registry_product' => 'productId', // * your product name/id ((your_productid))
 'registry_title' => 'Product Title', // your product title
 'registry_description' => 'Product Description', // your product description
 'registry_version' => 'M.m.p', // your product version
 'registry_license' => 'Lx', // 'L1'(Lite), 'L2'(Basic), 'L3'(Standard), 'L4'(Professional), 'L5'(Enterprise), 'LD'(Developer), 'LU'(Unlimited)
 'registry_count' => int, // Number of licenses (users/seats/devices)
 'registry_variations' => array('name'=>'value',...), // array of name/value pairs
 'registry_options' => array('value',...), // array of registry options
 'registry_domains' => array('domain',...), // array of valid/registered domains
 'registry_sites' => array('url',...), // array of valid/registered sites/uris
 'registry_transid' => '', // external transaction id
 'registry_timezone' => '', // standard timezone string (client timezone)
 'registry_locale' => '', // standard locale/language code
];
</code></pre>
* Required values (registry_key not required when creating a new registration).
<blockquote>
If setting registry_transid, the recommended (not required) format is <code>{id}|{source}|{suffix}</code> where {id} is the transaction id, {source} indicates the source of the transaction, and {suffix} may be used as needed.
</blockquote>
Any additional fields passed wil be saved as custom fields.
Although typically set by the Software Registry server, with the proper option setting, the API may override:
<pre><code>[
 'registry_status' => 'status', // 'pending', 'trial', 'active', 'inactive', 'expired', 'terminated'
 'registry_effective' => 'DD-MMM-YYYY', // Effective date
 'registry_expires' => 'DD-MMM-YYYY', // Expiration date or term ('30 days', '1 year',... added to effective date)
];
</code></pre>
Payment information may be posted with:
<pre><code>[
 'registry_paydue' => float, // amount to be paid/billed,
 'registry_payamount' => float, // amount paid,
 'registry_paydate' => 'DD-MMM-YYYY', // date paid
 'registry_payid' => 'payment id' // transaction id/check #, etc.
 'registry_nextpay' => 'DD-MMM-YYYY', // next payment/renewal date
];
</code></pre>
API Requests
Create/request a new registration…
<pre><code>$response = $this->registryApiRequest('create',$apiParams);
</code></pre>
Activate an existing registration…
<pre><code>$response = $this->registryApiRequest('activate',['registry_key' => '<registrationKeyValue>']);
</code></pre>
Activate and Update an existing registration…
<pre><code>$response = $this->registryApiRequest('activate',$apiParams);
</code></pre>
Deactivate an existing registration…
<pre><code>$response = $this->registryApiRequest('deactivate',['registry_key' => '<registrationKeyValue>']);
</code></pre>
Verify or Refresh an existing registration…
<pre><code>$response = $this->registryApiRequest('verify',['registry_key' => '<registrationKeyValue>']);
$response = $this->registryApiRequest('refresh',$apiParams);
</code></pre>
Revise an existing registration…
<pre><code>$response = $this->registryApiRequest('revise',$apiParams);
</code></pre>
API Response
The API response is a standard object. status->code is an http status, 200 indicating success.
<pre><code>status ->
(
 code -> 200, // HTTP status code
 message -> '(action) ok' // (action) = 'create', 'activate', 'deactivate', 'verify', 'revise'
),
registration ->
(
 registry_key -> string // UUID,
 registry_status -> string, // 'pending', 'trial', 'active', 'inactive', 'expired', 'terminated', 'invalid'
 registry_effective -> string, // DD-MMM-YYYY effective date
 registry_expires -> string, // DD-MMM-YYYY expiration date
 registry_name -> string,
 registry_email -> string,
 registry_company -> string,
 registry_address -> string,
 registry_phone -> string,
 registry_product -> string,
 registry_title -> string,
 registry_description -> string,
 registry_version -> string,
 registry_license -> string,
 registry_count -> int,
 registry_variations -> array,
 registry_options -> array,
 registry_domains -> array,
 registry_sites -> array,
 registry_transid -> string,
 registry_timezone -> string,
 registry_locale -> string,
 registry_valid -> bool,
),
registrar ->
(
 contact -> object(
 name -> string // Registrar Name
 email -> string // Registrar Support Email
 phone -> string // Registrar Telephone
 web -> string // Registrar Web Address
 ),
 timezone -> string, // standard timezone string
 locale -> string, // WordPress locale
 cacheTime -> int, // in seconds, time to cache the registration response (Default Cache Time)
 refreshInterval -> int, // in seconds, time before refreshing the registration (Default Refresh Time)
 refreshSchedule -> string, // 'hourly', 'twicedaily', 'daily', 'twiceweekly', 'weekly', 'twicemonthly', 'monthly' - corresponding to refreshInterval
 options -> array( // from settings page, registrar_options (Allow API to...)
 'allow_set_key',
 'allow_set_status',
 'allow_set_effective',
 'allow_set_expiration',
 'allow_activation_update'
 ),
 licenseCodes -> object( // may be changed by filter on registration server
 L1 -> 'Lite'
 L2 -> 'Basic'
 L3 -> 'Standard'
 L4 -> 'Professional'
 L5 -> 'Enterprise'
 LD -> 'Developer'
 LU -> 'Unlimited'
 ),
 notices -> object(
 info -> string, // information message text
 warning -> string, // warning message text
 error -> string, // error message text
 success -> string, // success message text
 ),
 message -> string, // html message
),
registryHtml -> string, // html (table) of human-readable registration values
supplemental -> mixed, // supplemental data/html assigned via filters (developer's discretion).
</code></pre>
On a successful response (status->code = 200), the SDK will automatically cache the registration data and schedule the next refresh event (you do not have to do this).
notices may be set (according to severity) to indicate an expiration or pending expiration and should be displayed to the user. Typically, only one notice will be set but they can be set via the <code>eacSoftwareRegistry_api_registration_notices</code> filter.
message is set via the <code>eacSoftwareRegistry_api_registration_message</code> filter.
supplemental is set via the <code>eacSoftwareRegistry_api_registration_supplemental</code> filter.
On an error response, an additional element is included:
<pre><code>error ->
(
 code -> 'error_code',
 message -> 'error message'
),
</code></pre>
error->message may be more informative than status->message. 
Errors may be handled with something like:
<pre><code>if ($this->is_api_error($response))
{
 echo "<div class='notice notice-error'><h4>Error ".$response->error->code." : ".$response->error->message."</h4></div>";
}
</code></pre>
<h4>Methods, Hooks, and Callbacks</h4>
Useful methods built into the SDK…
<pre><code>$this->isValidRegistration();
 // Returns boolean
 if ( $this->isValidRegistration() ) {...}

$this->getRegistrationKey();
 // Returns the current registration key
 $registrationKey = $this->getRegistrationKey();

$this->getCurrentRegistration();
 // Returns the current registration object (above response object)
 $currentRegistration = $this->getCurrentRegistration();

$this->isRegistryValue($keyName);
 // Returns the value of a specific registry key
 $regStatus = $this->isRegistryValue( 'status ');

$this->isRegistryValue($keyName, $value, $test);
 // Returns boolean comparison of the value of a registry key ($test is '=|eq' (default), '<|lt', '>|gt', '<=|le', '>=|ge')
 if ( $this->isRegistryValue('license', 'L3', '>=') ) {...}
</code></pre>
Several hooks are available to customize or react to registration events. 
In WordPresss, there are several actions and filters, for file based projects there are corresponding callback methods…
<pre><code> filter/callback: (your_productid)_api_remote_request( $request, $endpoint )
 @param array $request ['method'=>, 'timeout'=>, 'redirection'=>, 'sslverify'=>, 'headers'=>, 'body'=>]
 @param string $endpoint create, activate, deactivate, verify, refresh, revise
 @return array request body

 action/callback: (your_productid)_api_remote_response( $body, $request, $endpoint )
 @param array $body response body
 @param array $request ['method'=>, 'timeout'=>, 'redirection'=>, 'sslverify'=>, 'headers'=>, 'body'=>]
 @param string $endpoint create, activate, deactivate, verify, refresh, revise

 action/callback: (your_productid)_api_remote_$endpoint( $body, $request, $endpoint )
 @param array $body response body
 @param array $request ['method'=>, 'timeout'=>, 'redirection'=>, 'sslverify'=>, 'headers'=>, 'body'=>]
 @param string $endpoint create, activate, deactivate, verify, refresh, revise

 action/callback: (your_productid)_api_remote_error( $error, $request, $endpoint )
 @param object $error {status:{}, error: {}}
 @param array $request ['method'=>, 'timeout'=>, 'redirection'=>, 'sslverify'=>, 'headers'=>, 'body'=>]
 @param string $endpoint create, activate, deactivate, verify, refresh, revise

 action/callback: (your_productid)_update_registration($registration)
 @param array $registration registration object

 action/callback: (your_productid)_purge_registration()
</code></pre>
<h4>What You Need To Do</h4>
For WordPress Projects
In your class constructor/initialization, add an action to fulfill the registration refresh scheduled by the <code>scheduleRegistryRefresh()</code> method in <code>(your_productid).wordpress.trait.php</code>
<pre><code>\add_action( '(your_productid)_registry_refresh', array($this, 'refreshRegistration') );
</code></pre>
You can add this and other hooks with:
<pre><code>$this->addSoftwareRegistryHooks();
</code></pre>
The <code>addSoftwareRegistryHooks()</code> method adds:
<pre><code>\add_action( '(your_productid)_registry_refresh', array($this, 'refreshRegistration') );
\add_filter( '(your_productid)_is_registered', array($this, 'isValidRegistration') );
\add_filter( '(your_productid)_registration_key', array($this, 'getRegistrationKey') );
\add_filter( '(your_productid)_registration', array($this, 'getCurrentRegistration') );
\add_filter( '(your_productid)_registry_value', array($this, 'isRegistryValue'), 10, 4 );
</code></pre>
Example:
<pre><code>include "(your_productid)_registration/(your_productid)_registration.includes.php";

class <your_classname> implements \(your_namespace)\Interfaces\(your_productid)_registration
{
 use \(your_namespace)\Traits\(your_productid)_registration_wordpress;
 ...
 public function __construct()
 {
 $this->addSoftwareRegistryHooks();
 }
}
</code></pre>
Note:
If your primary plugin file name is not the same as the product id, edit your <code>(your_productid).interface.tpl</code> file and change the <code>SOFTWARE_REGISTRY_FILENAME</code> constant.
<pre><code> const SOFTWARE_REGISTRY_FILENAME = 'myPluginName';
</code></pre>
For Other File Based Projects
The <code>scheduleRegistryRefresh()</code> method in <code>(your_productid)_registration.filebased.trait.php</code> is called to schedule the next registration refresh. This method can be modified to schedule a cron event to execute the refresh at a future time. The scheduled event may run <code>(your_productid)_registration.refresh.php <registrationKeyValue></code> from the command line to refresh the registration.
When left as is, the <code>checkRegistryRefreshEvent()</code> method uses the key file to check for a needed registration refresh.
In your class constructor or destructor add:
<pre><code>$this->checkRegistryRefreshEvent();
</code></pre>
to trigger the refresh check.
Example:
<pre><code>include "(your_productid)_registration/(your_productid)_registration.includes.php";

class <your_classname> implements \(your_namespace)\Interfaces\(your_productid)_registration
{
 use \(your_namespace)\Traits\(your_productid)_registration_filebased;
 ...
 public function __destruct()
 {
 /* if necessary, set HOME/USERPROFILE and/or TMP/TMPDIR/TEMP directories */
 // putenv('HOME={your home directory}'); // where the registration key is stored, otherwise use $_SERVER['DOCUMENT_ROOT']
 // putenv('TMP={your temp directory}'); // where the registration data is stored, otherwise use sys_get_temp_dir()
 $this->checkRegistryRefreshEvent();
 }
}
</code></pre>
<h4>User Interface</h4>
Of course, the user interface is up to you, the developer, but you may look at (and maybe use) the registration UI trait included with {eac}Doojigger and used by {eac}SoftwareRegistry as an example.
see:
<ul>
<li>…/Traits/swRegistrationUI.trait.php in the eacDoojigger folder.</li>
<li>…/Extensions/class.eacSoftwareRegistry_registration.extension.php in the eacSoftwareRegistry folder.</li>
</ul>
<h4>See Also</h4>
<ul>
<li>
<a href="https://swregistry.earthasylum.com/software-registration-server/" rel="nofollow ugc">{eac}SoftwareRegistry – Software Registration Server</a>
</li>
<li>
<a href="https://swregistry.earthasylum.com/software-registry-hooks/" rel="nofollow ugc">{eac}SoftwareRegistry Custom Hooks</a>
</li>
</ul>
<h3>Copyright</h3>
<h4>Copyright © 2019-2025, EarthAsylum Consulting, distributed under the terms of the GNU GPL.</h4>
This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should receive a copy of the GNU General Public License along with this program. If not, see <a href="https://www.gnu.org/licenses/" rel="nofollow ugc">https://www.gnu.org/licenses/</a>.

{eac}SoftwareRegistry Distribution SDK

{eac}SoftwareRegistry Distribution SDK for the Software Registration Server - Implementing the Software Registry SDK Package.

{eac}SoftwareRegistry WooCommerce Webhook Endpoints vs {eac}SoftwareRegistry Distribution SDK