Disable domain fronting

Co-authored-by: jbdoumenjou <jb.doumenjou@gmail.com>

docs/content/migration/v2.md

@@ -1,5 +1,117 @@
 # Migration: Steps needed between the versions
 
+## v2.x to v2.2.2
+
+### Domain fronting
+
+In `v2.2.2` we introduced the ability to avoid [Domain fronting](https://en.wikipedia.org/wiki/Domain_fronting), 
+and enabled it by default for [https routers](../routing/routers/index.md#rule) configured with ```Host(`something`)```.
+
+!!! example "Allow Domain Fronting on a Specific Router"
+    
+    !!! info "Before v2.2.2"
+    
+    ```yaml tab="Docker"
+    labels:
+      - "traefik.http.routers.router0.rule=Host(`test.localhost`)"
+    ```
+    
+    ```yaml tab="K8s Ingress"
+    apiVersion: traefik.containo.us/v1alpha1
+    kind: IngressRoute
+    metadata:
+      name: ingressroutebar
+    
+    spec:
+      entryPoints:
+        - http
+      routes:
+      - match: Host(`test.localhost`)
+        kind: Rule
+        services:
+        - name: server0
+          port: 80
+        - name: server1
+          port: 80
+    ```
+        
+    ```toml tab="File (TOML)"
+    [http.routers.router0]
+        rule = "Host(`test.localhost`)"
+        service = "my-service"
+    ```
+    
+    ```toml tab="File (YAML)"
+    http:
+      routers:
+        router0:
+          rule: "Host(`test.localhost`)"
+          service: my-service
+    ```
+
+    !!! info "v2.2.2"
+    
+    ```yaml tab="Docker"
+    labels:
+      - "traefik.http.routers.router0.rule=HostHeader(`test.localhost`)"
+    ```
+    
+    ```yaml tab="K8s Ingress"
+    apiVersion: traefik.containo.us/v1alpha1
+    kind: IngressRoute
+    metadata:
+      name: ingressroutebar
+    
+    spec:
+      entryPoints:
+        - http
+      routes:
+      - match: HostHeader(`test.localhost`)
+        kind: Rule
+        services:
+        - name: server0
+          port: 80
+        - name: server1
+          port: 80
+    ```
+        
+    ```toml tab="File (TOML)"
+    [http.routers.router0]
+        rule = "HostHeader(`test.localhost`)"
+        service = "my-service"
+    ```
+    
+    ```toml tab="File (YAML)"
+    http:
+      routers:
+        router0:
+          rule: "HostHeader(`test.localhost`)"
+          service: my-service
+    ```
+
+As a fallback, a new flag is available as a global option:
+
+!!! example "Enabling Domain Fronting for All Routers"
+    
+    ```toml tab="File (TOML)"
+    # Static configuration
+    [global]
+      # Enabling domain fronting
+      insecureSNI = true
+    ```
+    
+    ```yaml tab="File (YAML)"
+    # Static configuration
+    global:
+      # Enabling domain fronting
+      insecureSNI: true
+    ```
+    
+    ```bash tab="CLI"
+    # Enabling domain fronting
+    --global.insecureSNI
+    ```
+
 ## v2.0 to v2.1
 
 ### Kubernetes CRD