docs: enhance supported proxies documentation (#2210)

This enhances the supported proxies documentation to be more comprehensive.

docs/_includes/head_custom.html

@@ -1,2 +1,4 @@
 <link rel="stylesheet"
       href="https://cdnjs.cloudflare.com/ajax/libs/github-fork-ribbon-css/0.2.3/gh-fork-ribbon.min.css" />
+<link rel="stylesheet"
+      href="https://fonts.googleapis.com/icon?family=Material+Icons" />

docs/_sass/custom/custom.scss

@@ -8,3 +8,12 @@
 .tbl-beta-stage {
     border-bottom-width: 3px !important;
 }
+.material-icons.green {
+    color: #56D364;
+}
+.material-icons.red {
+    color: #F85149;
+}
+.material-icons.orange {
+    color: #E3B341;
+}

docs/deployment/supported-proxies/nginx.md

@@ -1,14 +1,14 @@
 ---
 layout: default
-title: Nginx
+title: NGINX
 parent: Proxy Integration
 grand_parent: Deployment
 nav_order: 2
 ---
 
-# Nginx
+# NGINX
 
-[nginx] is a reverse proxy supported by **Authelia**.
+[NGINX] is a reverse proxy supported by **Authelia**.
 
 ## Configuration
 
@@ -352,4 +352,4 @@ error_page 401 /authelia-redirect?rd=$target_url;
 
 This tells nginx to use the virtual endpoint we defined above in case the auth_request failed.
 
-[nginx]: https://www.nginx.com/
+[NGINX]: https://www.nginx.com/

docs/home/supported-proxies.md

@@ -5,13 +5,93 @@ parent: Home
 nav_order: 2
 ---
 
-The following reverse proxies are currently supported:
+The following table is a support matrix for Authelia features and specific reverse proxies.
 
-* NGINX
+|Proxy        |[Standard Support](#standard)                                                                          |[Kubernetes Support](#kubernetes)                                                               |[XHR Redirect](#xhr-redirect)                         |[Request Method](#request-method)                     |
-* Traefik
+|:-----------:|:-----------------------------------------------------------------------------------------------------:|:----------------------------------------------------------------------------------------------:|:----------------------------------------------------:|:----------------------------------------------------:|
-* HAProxy
+|[NGINX]      |[<span class="material-icons green">check_circle</span>](../deployment/supported-proxies/nginx.md)     |[<span class="material-icons green">check_circle</span>](../deployment/deployment-kubernetes.md)|<span class="material-icons red">cancel</span>        |<span class="material-icons green">check_circle</span>|
+|[Traefik] 1.x|[<span class="material-icons green">check_circle</span>](../deployment/supported-proxies/traefik1.x.md)|<span class="material-icons orange">error</span>                                                |<span class="material-icons green">check_circle</span>|<span class="material-icons green">check_circle</span>|
+|[Traefik] 2.x|[<span class="material-icons green">check_circle</span>](../deployment/supported-proxies/traefik2.x.md)|[<span class="material-icons green">check_circle</span>](../deployment/deployment-kubernetes.md)|<span class="material-icons green">check_circle</span>|<span class="material-icons green">check_circle</span>|
+|[HAProxy]    |[<span class="material-icons green">check_circle</span>](../deployment/supported-proxies/haproxy.md)   |<span class="material-icons red">cancel</span>                                                  |<span class="material-icons orange">error</span>      |<span class="material-icons green">check_circle</span>|
+|[Envoy]      |<span class="material-icons orange">error</span>                                                       |<span class="material-icons orange">error</span>                                                |<span class="material-icons orange">error</span>      |<span class="material-icons orange">error</span>      |
+|[Caddy] 2.x  |<span class="material-icons orange">error</span>                                                       |<span class="material-icons red">cancel</span>                                                  |<span class="material-icons orange">error</span>      |<span class="material-icons orange">error</span>      |
+|[Apache]     |<span class="material-icons red">cancel</span>                                                         |<span class="material-icons red">cancel</span>                                                  |<span class="material-icons red">cancel</span>        |<span class="material-icons red">cancel</span>        |
+|[IIS]        |<span class="material-icons red">cancel</span>                                                         |<span class="material-icons red">cancel</span>                                                  |<span class="material-icons red">cancel</span>        |<span class="material-icons red">cancel</span>        |
 
-Those proxies are also supported on Kubernetes using their related ingress controller.
+<span class="material-icons green">check_circle</span> *Support confirmed, additionally these icons are links to documentation for both the Standard and Kubernetes support columns*
 
-For more details on the deployment on Kubernetes, please refer
+<span class="material-icons orange">error</span> *Support is likely and being investigated*
-to [this documentation](../deployment/deployment-kubernetes.md).
+
+<span class="material-icons red">cancel</span> *Either not supported or unlikely to be supported*
+
+## Support
+
+### Standard
+
+Standard support includes the essential features in securing an application with Authelia such as:
+
+- Redirecting users to the Authelia portal if they are not authenticated.
+- Redirecting users to the target application after authentication has occurred successfully.
+
+It does not include actually running Authelia as a service behind the proxy, any proxy should be compatible with serving
+the Authelia portal itself. Standard support is only important for protected applications.
+
+### Kubernetes
+
+While proxies that generally support Authelia outside a [Kubernetes] cluster, there are a few situations where that does
+not translate to being possible when used as an [Ingress Controller]. There are various reasons for this such as the
+reverse proxy in question does not even support running as a [Kubernetes] [Ingress Controller], or the required modules
+to perform authentication transparently to the user are not typically available inside a cluster.
+
+More information about [Kubernetes] deployments of Authelia can be read in the 
+[documentation](../deployment/deployment-kubernetes.md).
+
+### XHR Redirect
+
+XML HTTP Requests do not typically redirect browsers when returned 30x status codes. Instead, the standard method is to
+return a 401 status code with a Location header. While this may seem trivial; currently there isn't wide support for it.
+For example nginx's ngx_http_auth_request_module does not seem to support this in any way.
+
+### Request Method
+
+Authelia detects the upstream request method using the X-Forwarded-Method header. Some proxies set this out of the box,
+some require you to configure this manually. At the present time all proxies that have 
+[Standard Support](#standard-support) do support this.
+
+## Specific proxy notes
+
+### HAProxy
+
+[HAProxy] is only supported via a lua [module](https://github.com/haproxytech/haproxy-lua-http). Lua is typically not 
+available in [Kubernetes]. You would likely have to build your own [HAProxy] image.
+
+### Envoy
+
+[Envoy] is currently not documented however we believe it is likely to be technically supported. This should be possible
+via [Envoy]'s [external authorization](https://www.envoyproxy.io/docs/envoy/latest/api-v3/extensions/filters/http/ext_authz/v3/ext_authz.proto.html#extensions-filters-http-ext-authz-v3-extauthz).
+
+### Caddy
+
+[Work](https://github.com/authelia/caddy-forwardauth) is being done to support Caddy 2.x, however this is a low 
+priority. You can see the progress and try it for yourself if you're interested. Regular feedback would accelerate this
+work.
+
+### Apache
+
+[Apache] has no module that supports this kind of authentication method. It's not certain this would even be possible,
+however if anyone did something like this in the past we'd be interested in a contribution.
+
+### IIS
+
+Microsoft [IIS] not currently supported since no auth module exists for this purpose out-of-the-box or from any known
+third party. It's likely possible but unlikely to be highly used so there is little to be gained by supporting this proxy.
+
+[NGINX]: https://www.nginx.com/
+[Traefik]: https://traefik.io/
+[HAProxy]: https://www.haproxy.com/
+[Envoy]: https://www.envoyproxy.io/
+[Caddy]: https://caddyserver.com/
+[Apache]: https://httpd.apache.org/
+[IIS]: https://www.iis.net/
+[Kubernetes]: https://kubernetes.io/
+[Ingress Controller]: https://kubernetes.io/docs/concepts/services-networking/ingress-controllers/