Add OAuth2AuthenticatedPrincipal Link

Fixes gh-7406

Author: jzheaux

docs/manual/src/docs/asciidoc/_includes/reactive/oauth2/resource-server.adoc

@@ -608,7 +608,7 @@ Given an Opaque Token, Resource Server will
 2. Inspect the response for an `{ 'active' : true }` attribute
 3. Map each scope to an authority with the prefix `SCOPE_`
 
-The resulting `Authentication#getPrincipal`, by default, is a Spring Security `OAuth2AuthenticatedPrincipal` object, and `Authentication#getName` maps to the token's `sub` property, if one is present.
+The resulting `Authentication#getPrincipal`, by default, is a Spring Security `{security-api-url}org/springframework/security/oauth2/core/OAuth2AuthenticatedPrincipal.html[OAuth2AuthenticatedPrincipal]` object, and `Authentication#getName` maps to the token's `sub` property, if one is present.
 
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docs/manual/src/docs/asciidoc/_includes/servlet/oauth2/oauth2-resourceserver.adoc

@@ -746,7 +746,7 @@ Given an Opaque Token, Resource Server will
 2. Inspect the response for an `{ 'active' : true }` attribute
 3. Map each scope to an authority with the prefix `SCOPE_`
 
-The resulting `Authentication#getPrincipal`, by default, is a Spring Security `OAuth2AuthenticatedPrincipal` object, and `Authentication#getName` maps to the token's `sub` property, if one is present.
+The resulting `Authentication#getPrincipal`, by default, is a Spring Security `{security-api-url}org/springframework/security/oauth2/core/OAuth2AuthenticatedPrincipal.html[OAuth2AuthenticatedPrincipal]` object, and `Authentication#getName` maps to the token's `sub` property, if one is present.
 
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