Fixes#9549
* Not a full UE pass on the group of external provider topics ... don't quite have time for that right now. However, I do hit a number of small UE-type updates.
* Engineering: You only need to look at one thing here: See the *forwarded-headers-middleware.md* file. The content of the file is below. The INCLUDE is linked into the external auth provider topics to surface Forwarded Headers Middleware (proxy/LB topic).
> \#\# Forward request information with a proxy or load balancer
>
> If the app is deployed behind a proxy server or load balancer, some of the original request information might be forwarded to the app in request headers. This information usually includes the secure request scheme (\`https\`), host, and client IP address. Apps don't automatically read these request headers to discover and use the original request information.
>
> The scheme is used in link generation that affects the authentication flow with external providers. Losing the secure scheme (\`https\`) results in the app generating incorrect insecure redirect URLs.
>
> Use Forwarded Headers Middleware to make the original request information available to the app for request processing.
>
> For more information, see \<xref:host-and-deploy/proxy-load-balancer>.
If it's easier to provide feedback in a comment here over hunting down the file on the diff, that works for me.
8031f63a22