ServerCertificateSelectionCallback - update documentation (#4351)

* ServerCertificateSelectionCallback - update documentation

* Apply suggestions from code review

Co-authored-by: Maira Wenzel <[email protected]>

* Apply PR comments

Co-authored-by: Jan Jahoda <[email protected]>
Co-authored-by: Maira Wenzel <[email protected]>

Author: 3 people

xml/System.Net.Security/ServerCertificateSelectionCallback.xml

@@ -29,10 +29,20 @@
     <ReturnType>System.Security.Cryptography.X509Certificates.X509Certificate</ReturnType>
   </ReturnValue>
   <Docs>
-    <param name="sender">To be added.</param>
-    <param name="hostName">To be added.</param>
-    <summary>To be added.</summary>
-    <returns>To be added.</returns>
-    <remarks>To be added.</remarks>
+    <param name="sender">A <see cref="T:System.Net.Security.SslStream" /> object.</param>
+    <param name="hostName">The host name requested by the client. If the client doesn't use the host_name TLS extension, the <paramref name="hostName" /> is an empty string.</param>   
+    <summary>Selects the server Secure Sockets Layer (SSL) certificate.</summary>
+    <returns>An <see cref="T:System.Security.Cryptography.X509Certificates.X509Certificate" /> used for establishing an SSL connection.</returns>
+    <remarks>
+      <format type="text/markdown"><![CDATA[  
+  
+## Remarks  
+
+The server uses this delegate to select a server connection certificate.
+
+This delegate is used by the <xref:System.Net.Security.SslStream> class. The <xref:System.Net.Security.SslStream> class is used to help secure information exchanged between a client and server.
+
+ ]]></format>
+    </remarks>
   </Docs>
 </Type>