Guide: move api intro to main guide

Author: distantnative

content/docs/1_guide/20_api/1_introduction/guide.txt

@@ -2,7 +2,7 @@ Title: Data
 
 ----
 
-Intro: Once you start (link: docs/guide/api/introduction#further-customize-the-api text: customizing the API) and adding your own API endpoints, there is a lot to know about how to interact with data in the callback functions.
+Intro: Once you start (link: docs/guide/api#further-customize-the-api text: customizing the API) and adding your own API endpoints, there is a lot to know about how to interact with data in the callback functions.
 
 ----
 

content/docs/1_guide/20_api/3_data/guide.txt

@@ -10,4 +10,84 @@ Category: Extending Kirby
 
 ----
 
-Icon: cloud
+Intro: Kirby's REST API is used by the (glossary: Panel) to connect between the (glossary: Vue) frontend and the PHP backend. It offers full access to your site, pages, files, users and more. You can use it for your SPA or mobile applications built on top of Kirby.
+
+----
+
+Text:
+
+## Endpoints
+There are a large number of endpoints, split into the following areas:
+
+(reference: api)
+
+## Authentication
+
+Every API request requires authentication. We offer session-based authentication or HTTP Basic auth. (link: docs/guide/api/authentication text: Read more ›)
+
+## Language
+In a (link: docs/guide/languages text: multi-language site) it is necessary to specify the language for which you want to use the API. This is done by sending an `X-Language` header containing the desired language code with your request.
+
+## Errors
+
+### Example error
+
+```js
+{
+    "status": "error",
+    "message": "The page \"example\" cannot be found",
+    "code": 404
+}
+```
+
+### In debug mode
+
+When debug mode is activated in your config, you will get a more detailed error response with the exception type, file and line.
+
+```js
+{
+    "status": "error",
+    "exception": "Exception",
+    "message": "The page \"example\" cannot be found",
+    "file": "config/api/data.php",
+    "line": 46,
+    "code": 500
+}
+```
+
+To activate the debug mode, add the following to your config:
+
+```php "/site/config/config.php"
+return [
+  'debug' => true
+];
+```
+
+<warning>
+Please make sure to disable `debug` mode in production! Displaying PHP errors on a public server can be a serious security risk:
+
+- Error messages are displayed with detailed information about the code structure (e.g. file path, class, method)
+- With Whoops enabled, there will be even more detailed information about the code structure
+- Detailed error messages for login failures could leak information to attackers
+
+In a production environment, always log errors to your PHP error logs.
+</warning>
+
+
+## Custom API location
+
+Kirby can be configured to host the API at a different location. This can be set up in your config.
+
+```php "/site/config/config.php"
+return [
+  'api' => [
+    'slug' => 'rest'
+  ]
+];
+```
+
+All API endpoints are now available at `https://yourdomain.com/rest`. The Panel will automatically switch to the new API location.
+
+## Further customize the API
+
+Find out how you can define custom endpoints, data functions, models etc. either via your (link: docs/reference/system/options/api text: config options ›) or (link: docs/reference/plugins/extensions/api text: in a plugin ›).

content/docs/1_guide/20_api/guide.txt

@@ -94,7 +94,7 @@ Using the REST API is the way to go if you want to modify data.
 
 ### Documentation
 
-- (link: docs/guide/api/introduction text: Using the REST API)
+- (link: docs/guide/api text: Using the REST API)
 - (link: docs/guide/api/authentication text: REST API authentication method)
 - (link: docs/reference/api text: API endpoint reference)
 - (link: docs/reference/plugins/extensions/api text: Custom API endpoints and data providers)

content/docs/1_guide/22_beyond-kirby/guide.txt

@@ -35,7 +35,7 @@ Kirby::plugin('my/api', [
 
 Your new endpoint is now available at `https://yourdomain.com/api/my-endpoint` and will return a json encoded version of the returned array.
 
-The endpoint is automatically protected with the same authentication layer as our own endpoints. It will also move when you (link: docs/guide/api/introduction#custom-api-location text: change the API slug).
+The endpoint is automatically protected with the same authentication layer as our own endpoints. It will also move when you (link: docs/guide/api#custom-api-location text: change the API slug).
 
 ### Access to `$kirby`
 

content/docs/2_reference/7_plugins/1_extensions/0_api/reference-extension.txt

@@ -14,7 +14,7 @@ Text:
 
 ## What makes a field plugin?
 
-Our Kirby panel is built with (glossary: vue) and speaks to our (link: docs/guide/api/introduction text: REST API). Your field plugin needs to consist out of **three parts**:
+Our Kirby panel is built with (glossary: vue) and speaks to our (link: docs/guide/api text: REST API). Your field plugin needs to consist out of **three parts**:
 
 - PHP code for the REST API: `index.php`
 - Vue code for the panel: `index.js`

content/docs/2_reference/7_plugins/1_extensions/0_fields/reference-extension.txt

@@ -76,7 +76,7 @@ We've overhauled our entire plugin system and built a more reliable and consiste
 
 Kirby 3 has a built in REST API. You can comfortably create and edit your content in the Panel, and then consume your content in SPAs, mobile applications or static site generators.
 
-(link: docs/guide/api/introduction text: Learn more ›)
+(link: docs/guide/api text: Learn more ›)
 
 ## Virtual pages & external data sources