Update single-sign-on-saml-protocol.md

Corrected two items in the docs to match actual Azure AD behavior.   Signed requests are supported but not validated,   Subject elements in requests are not supported and will result in an error rather than being ignored.

Author: paulgarn

articles/active-directory/develop/single-sign-on-saml-protocol.md

@@ -89,10 +89,10 @@ The `Scoping` element, which includes a list of identity providers, is optional
 If provided, don't include the `ProxyCount` attribute, `IDPListOption` or `RequesterID` element, as they aren't supported.
 
 ### Signature
-Don't include a `Signature` element in `AuthnRequest` elements, as Azure AD does not support signed authentication requests.
+Don't include a `Signature` element in `AuthnRequest` elements. Azure AD does not validate signed authentication requests. Requestor verification is provided for by only responding to registered Assertion Consumer Service URLs.
 
 ### Subject
-Azure AD ignores the `Subject` element of `AuthnRequest` elements.
+Don't include a `Subject` element. Azure AD doesn't support specifying a subject for a request and will return an error if one is provided.
 
 ## Response
 When a requested sign-on completes successfully, Azure AD posts a response to the cloud service. A response to a successful sign-on attempt looks like the following sample: