Create How to use Re2o/How to use Autoregistration

How-to-use-Re2o/How-to-use-Autoregistration.md

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+Re2o can allow your users to auto-register. Either using WiFi or using wired connection.
+
+# Wired Connection
+
+Currently, the following switch brands are supported :
+*  HP
+*  Juniper
+
+## Autoregister view
+
+The goal is to lead your user toward `http://your.website/users/initial_register`.
+
+The query must have the following `GET` parameters :
+
+| Parameter name | content |
+| ------ | ------ |
+| `switch_ip` | IP address of the switch |
+| `switch_port` | The port to which the client is connected | 
+| `client_mac` | The mac address of the client |
+
+## On Juniper
+
+We tweak [Central Web Authentication](https://www.juniper.net/documentation/en_US/junos/topics/topic-map/central-web-authentication.html). 
+
+We will configure the RADIUS server in order to send responses in the form of 
+
+```
+001122334455 Auth-Type := EAP, Cleartext-Password :="001122334455"
+        Session-Timeout = "300",
+        Juniper-CWA-Redirect-URL = "https://your.ser.ver.ip/?get_parameters",
+        Filter-Id = "JNPR_RSVD_FILTER_CWA",
+```
+
+To do that, we can configure our RADIUS server in `http://your.website/users/preferences` in order to get the following configuration, where `Adhérents` is the VLAN for accepted users and `Prérézotage` an intermediary VLAN for unregistered users and machines.
+
+ ![radius_config_re2o](uploads/1dd63f4a8499335ee591545ece565ccb/radius_config_re2o.jpg)
+
+Note that you must provide a DHCP server on the VLAN for unregistered users and machines. If you want your users to pay their membership, you should also provide them with a way to contact the payment service.
+
+## On HP
+
+todo
+
+# WiFi
+
+todo