Documentation Revamp

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

docs/content/middlewares/forwardauth.md

@@ -0,0 +1,63 @@
+# ForwardAuth
+
+Using an External Service to Ccheck for Credentials
+{: .subtitle }
+
+![AuthForward](../assets/img/middleware/authforward.png)
+
+The ForwardAuth middleware delegate the authentication to an external service.
+If the service response code is 2XX, access is granted and the original request is performed.
+Otherwise, the response from the authentication server is returned.
+
+## Configuration Examples
+
+??? example "File -- Forward authentication to authserver.com"
+
+    ```toml
+    [Middlewares]
+      [Middlewares.test-auth.forwardauth]
+        address = "https://authserver.com/auth"
+        trustForwardHeader = true
+        authResponseHeaders = ["X-Auth-User", "X-Secret"]
+
+        [Middlewares.test-auth.forwardauth.tls]
+          ca = "path/to/local.crt"
+          caOptional = true
+          cert = "path/to/foo.cert"
+          key = "path/to/foo.key"      
+    ```
+
+??? example "Docker -- Forward authentication to authserver.com"
+
+    ```yml
+    a-container:
+          image: a-container-image 
+            labels:
+              - "traefik.Middlewares.test-auth.ForwardAuth.Address=https://authserver.com/auth"
+              - "traefik.Middlewares.test-auth.ForwardAuth.AuthResponseHeaders=X-Auth-User, X-Secret"
+              - "traefik.Middlewares.test-auth.ForwardAuth.TLS.CA=path/to/local.crt"
+              - "traefik.Middlewares.test-auth.ForwardAuth.TLS.CAOptional=true"
+              - "traefik.Middlewares.test-auth.ForwardAuth.TLS.Cert=path/to/foo.cert"
+              - "traefik.Middlewares.test-auth.ForwardAuth.TLS.InsecureSkipVerify=true"
+              - "traefik.Middlewares.test-auth.ForwardAuth.TLS.Key=path/to/foo.key"
+              - "traefik.Middlewares.test-auth.ForwardAuth.TrustForwardHeader=true"
+              		
+    ```
+
+## Configuration Options
+
+### address
+
+The `address` option defines the authentication server address.
+
+### trustForwardHeader
+
+Set the `trustForwardHeader` option to true to trust all the existing X-Forwarded-* headers.
+
+### authResponseHeaders
+
+The `authResponseHeaders` option is the list of the headers to copy from the authentication server to the request.
+
+### tls
+
+The `tls` option is the tls configuration from Traefik to the authentication server.