Add Legrand Home+ Control Integration document (#16644)

Co-authored-by: Klaas Schoute <klaas_schoute@hotmail.com>
Co-authored-by: Franck Nijhof <frenck@frenck.nl>

source/_integrations/home_plus_control.markdown

@@ -0,0 +1,89 @@
+---
+title: Legrand Home+ Control
+description: Instructions on how to integrate Legrand Home+ Control into Home Assistant.
+ha_category:
+  - Switch
+ha_release: 2021.4
+ha_iot_class: Cloud Polling
+ha_codeowners:
+  - '@chemaaa'
+ha_config_flow: true
+ha_domain: home_plus_control
+---
+
+The Home+ Control integration platform allows you to control a range of Legrand in-wall switches and power outlets that have smart home functionality thanks to their "with Netatmo" capabilities. 
+
+This integration works against the Home+ Control API, which is one of the many APIs offered through the [*Works with Legrand*](https://developer.legrand.com/) program. The API is capable of managing "Legrand/Btcino with Netatmo" devices, such as light switches, power outlets and rolling shutters.
+
+The devices that this API can manage are offered in different designs across different countries. The details of these can be found [here](https://developer.legrand.com/solutions/wiring-devices-with-netatmo/).
+
+This Home+ Control integration for Home Assistant currently has support for the following devices: 
+- Light switches
+- Power outlets
+
+In both cases, the devices are modeled as on/off switches within Home Assistant.
+
+This integration has been tested to work with the following range of Legrand products:
+- Valena Next™ with Netatmo
+
+
+## Authentication
+
+Before you are able to configure the Legrand Home + Control integration into Home Assistant, you must register with the *Works with Legrand* platform.
+
+These Legrand APIs rely on Oauth2 authentication, so you must follow these steps to obtain the necessary authentication parameters:
+
+1. Register an account at <https://developer.legrand.com>.
+2. Create a subscription to the *Starter Kit* (currently the only subscription available) and this will generate your `SUBSCRIPTION_KEY`.
+3. Register an application, where you will have to define a name, a redirect URL and the scopes of your application. When selecting the scopes, be sure to include all of the `.read` scopes, as well as the `light.write` and `plug.write` scopes to be able to control these modules from the integration.
+
+Once the registered application is confirmed, you should receive an email containing the `CLIENT_IDENTIFIER` and the `CLIENT_SECRET` which you will be using to set up the authentication flows. The application confirmation email is usually received within a few hours of having issued the request.
+
+Finally, to set up Oauth2 authentication in Home Assistant you should add the following information to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+home_plus_control:
+  client_id: CLIENT_IDENTIFIER
+  client_secret: CLIENT_SECRET
+  subscription_key: SUBSCRIPTION_KEY
+```
+
+{% configuration %}
+client_id:
+  description: Client identifier for your registered application on the *Works with Legrand* platform. Received via email.
+  required: true
+  type: string
+client_secret:
+  description: Client secret for your registered application on the *Works with Legrand* platform. Received via email.
+  required: true
+  type: string
+subscription_key:
+  description: Subscription identifier for your registered account on the *Works with Legrand* platform. Provided upon registration.
+  required: true
+  type: string
+{% endconfiguration %}
+
+
+At this point, you are now ready to add the Home+ Control integration to your Home Assistant instance as described in the [Configuration](#configuration) section.
+
+
+{% include integrations/config_flow.md %}
+
+
+## API Nomenclature
+
+Within the context of the Home+ Control API you may come across the following terms:
+
+* *Plant*: This is the term used to represent a *home* that holds the Legrand devices. In practice, a *plant* is represented by the *Legrand Home+ Control* gateway that acts as the central hub of the rest of the devices in the home network (uses Zigbee).
+* *Module*: This is the term used to represent a generic device within the *plant*, i.e., a light, a plug, a remote, etc.
+* *Light*: This is the term used to represent a light switch (or a micro-module). It is not modeled as your usual light entity because there are no brightness, color, etc. controls. It is modeled as an on/off switch.
+* *Plug*: This is the term used to represent a power outlet.
+
+Other devices that are mentioned in the API, but that are not currently supported by this integration are: *remotes* (wireless switches), *heaters* and *automations*.
+
+## API Limitations
+
+As described in the [authentication](#authentication) section, this integration requires you to set up a subscription in the *Works with Legrand* platform. 
+
+Currently, end-users only have access to the *Starter Kit* subscription which has a major limitation in the number of allowed API requests that are allowed - only 500 API calls per day (counter is reset at 00:00 every day). If this daily quota is ever exceeded, the API will report `403 Forbidden` HTTP responses.