Add information on preflight requests in CORS subsection

docs/api.rst

@@ -2705,6 +2705,36 @@ CORS
 
 PostgREST sets highly permissive cross origin resource sharing, that is why it accepts Ajax requests from any domain.
 
+It also handles `preflight requests <https://developer.mozilla.org/en-US/docs/Glossary/Preflight_request>`_ done by the browser, which are cached using the returned ``Access-Control-Max-Age: 86400`` header (86400 seconds = 24 hours). This is useful to reduce the latency of the subsequent requests.
+
+A ``POST`` preflight request would look like this:
+
+.. tabs::
+
+  .. code-tab:: http
+
+     OPTIONS /items HTTP/1.1
+     Origin: http://example.com
+     Access-Control-Allow-Method: POST
+     Access-Control-Allow-Headers: Content-Type
+
+  .. code-tab:: bash Curl
+
+     curl -i "http://localhost:3000/items" \
+       -X OPTIONS \
+       -H "Origin: http://example.com" \
+       -H "Access-Control-Request-Method: POST" \
+       -H "Access-Control-Request-Headers: Content-Type"
+
+.. code-block:: http
+
+  HTTP/1.1 200 OK
+  Access-Control-Allow-Origin: http://example.com
+  Access-Control-Allow-Credentials: true
+  Access-Control-Allow-Methods: GET, POST, PATCH, PUT, DELETE, OPTIONS, HEAD
+  Access-Control-Allow-Headers: Authorization, Content-Type, Accept, Accept-Language, Content-Language
+  Access-Control-Max-Age: 86400
+
 .. _multiple-schemas:
 
 Switching Schemas

postgrest.dict

@@ -127,6 +127,7 @@ PostgREST
 postgrest
 PostgREST's
 pre
+preflight
 psql
 Qin
 RabbitMQ