Deprecate caOptional option in client TLS configuration

docs/content/middlewares/http/forwardauth.md

@@ -426,70 +426,6 @@ http:
       ca = "path/to/local.crt"
 ```
 
-#### `caOptional`
-
-_Optional_
-
-The value of `caOptional` defines which policy should be used for the secure connection with TLS Client Authentication to the authentication server.
-
-!!! warning ""
-
-    If `ca` is undefined, this option will be ignored, and no client certificate will be requested during the handshake. Any provided certificate will thus never be verified.
-
-When this option is set to `true`, a client certificate is requested during the handshake but is not required. If a certificate is sent, it is required to be valid.
-
-When this option is set to `false`, a client certificate is requested during the handshake, and at least one valid certificate should be sent by the client.
-
-```yaml tab="Docker"
-labels:
-  - "traefik.http.middlewares.test-auth.forwardauth.tls.caOptional=true"
-```
-
-```yaml tab="Kubernetes"
-apiVersion: traefik.containo.us/v1alpha1
-kind: Middleware
-metadata:
-  name: test-auth
-spec:
-  forwardAuth:
-    address: https://example.com/auth
-    tls:
-      caOptional: true
-```
-
-```yaml tab="Consul Catalog"
-- "traefik.http.middlewares.test-auth.forwardauth.tls.caOptional=true"
-```
-
-```json tab="Marathon"
-"labels": {
-  "traefik.http.middlewares.test-auth.forwardauth.tls.caOptional": "true"
-}
-```
-
-```yaml tab="Rancher"
-labels:
-  - "traefik.http.middlewares.test-auth.forwardauth.tls.caOptional=true"
-```
-
-```yaml tab="File (YAML)"
-http:
-  middlewares:
-    test-auth:
-      forwardAuth:
-        address: "https://example.com/auth"
-        tls:
-          caOptional: true
-```
-
-```toml tab="File (TOML)"
-[http.middlewares]
-  [http.middlewares.test-auth.forwardAuth]
-    address = "https://example.com/auth"
-    [http.middlewares.test-auth.forwardAuth.tls]
-      caOptional = true
-```
-
 #### `cert`
 
 _Optional_