fix broken reference links

Author: duongau

articles/frontdoor/apex-domain.md

@@ -45,7 +45,7 @@ For example, suppose you want to use the apex domain `contoso.com` with Azure Fr
 | Record value | *use the value provided by Azure Front Door* |
 | Time to live (TTL) | 1 hour |
 
-## Azure Front Door-managed Transport Layer Security (TLS) certificate rotation
+## Azure Front Door-managed TLS certificate rotation
 
 When you use an Azure Front Door-managed certificate, Azure Front Door attempts to automatically rotate (renew) the certificate. Before it does so, Azure Front Door checks whether the DNS CNAME record is still pointed to the Azure Front Door endpoint. Apex domains don't have a CNAME record pointing to an Azure Front Door endpoint, so the autorotation for managed certificate fails until the domain ownership is revalidated.
 

articles/frontdoor/front-door-http-headers-protocol.md

@@ -24,7 +24,7 @@ Azure Front Door accepts most headers for the incoming request without modifying
 
 The debug request header, `X-Azure-DebugInfo`, provides extra debugging information about the Front Door. You need to send `X-Azure-DebugInfo: 1` request header from the client to the Azure Front Door to receive [optional response headers](#optional-debug-response-headers) when Azure Front Door response to the client. 
 
-## From Azure Front Door to the backend
+## From Front Door to the backend
 
 Azure Front Door includes headers for an incoming request unless they're removed because of restrictions. Azure Front Door also appends the following headers: