prevent pointless session start in webapi scope

Author: Maciej Pawłowski

app/code/Magento/Customer/etc/webapi_rest/di.xml

@@ -13,7 +13,7 @@
         <arguments>
             <argument name="userContexts" xsi:type="array">
                 <item name="customerSessionUserContext" xsi:type="array">
-                    <item name="type" xsi:type="object">Magento\Customer\Model\Authorization\CustomerSessionUserContext</item>
+                    <item name="type" xsi:type="object">Magento\Customer\Model\Authorization\CustomerSessionUserContext\Proxy</item>
                     <item name="sortOrder" xsi:type="string">20</item>
                 </item>
             </argument>

app/code/Magento/PageCache/etc/di.xml

@@ -37,9 +37,6 @@
             <argument name="layoutCacheKey" xsi:type="object">Magento\Framework\View\Layout\LayoutCacheKeyInterface</argument>
         </arguments>
     </type>
-    <type name="Magento\Framework\App\FrontControllerInterface">
-        <plugin name="page_cache_from_key_from_cookie" type="Magento\PageCache\Plugin\RegisterFormKeyFromCookie" />
-    </type>
     <preference for="Magento\PageCache\Model\VclGeneratorInterface" type="Magento\PageCache\Model\Varnish\VclGenerator"/>
     <preference for="Magento\PageCache\Model\VclTemplateLocatorInterface" type="Magento\PageCache\Model\Varnish\VclTemplateLocator"/>
 </config>

app/code/Magento/PageCache/etc/frontend/di.xml

@@ -9,6 +9,7 @@
     <type name="Magento\Framework\App\FrontControllerInterface">
         <plugin name="front-controller-builtin-cache" type="Magento\PageCache\Model\App\FrontController\BuiltinPlugin"/>
         <plugin name="front-controller-varnish-cache" type="Magento\PageCache\Model\App\FrontController\VarnishPlugin"/>
+        <plugin name="page_cache_from_key_from_cookie" type="Magento\PageCache\Plugin\RegisterFormKeyFromCookie" />
     </type>
     <type name="Magento\Framework\Controller\ResultInterface">
         <plugin name="result-builtin-cache" type="Magento\PageCache\Model\Controller\Result\BuiltinPlugin"/>

app/code/Magento/User/etc/webapi_rest/di.xml

@@ -10,7 +10,7 @@
         <arguments>
             <argument name="userContexts" xsi:type="array">
                 <item name="adminSessionUserContext" xsi:type="array">
-                    <item name="type" xsi:type="object">Magento\User\Model\Authorization\AdminSessionUserContext</item>
+                    <item name="type" xsi:type="object">Magento\User\Model\Authorization\AdminSessionUserContext\Proxy</item>
                     <item name="sortOrder" xsi:type="string">30</item>
                 </item>
             </argument>