Ensure that Read is compliant with xenc xsd schema

* KeyInfo could be empty (self-closing) element - don't attempt to read
* EncryptionMethod supports any element as a child. Log and Skip
everything except DigestMethod
* (Data/Key) Reference supports any element as a child. As we care only
about URI attribute - skip child elements that might appear
* Add tests for above cases

Author: GeoK

src/Microsoft.IdentityModel.Xml/EncryptedReference.cs

@@ -67,7 +67,7 @@ internal virtual void ReadXml(XmlDictionaryReader reader)
             if (reader.IsStartElement(XmlEncryptionConstants.Elements.KeyReference, XmlEncryptionConstants.Namespace) || reader.IsStartElement(XmlEncryptionConstants.Elements.DataReference, XmlEncryptionConstants.Namespace))
             {
                 Uri = reader.GetAttribute(XmlEncryptionConstants.Attributes.Uri, null);
-                reader.Read();
+                reader.Skip();
             }
         }
     }

src/Microsoft.IdentityModel.Xml/EncryptionMethod.cs

@@ -106,13 +106,13 @@ internal void ReadXml(XmlDictionaryReader reader)
                     if (reader.IsStartElement(XmlSignatureConstants.Elements.DigestMethod, XmlSignatureConstants.Namespace))
                     {
                         DigestMethod = reader.GetAttribute(XmlSignatureConstants.Attributes.Algorithm, null);
-                        reader.Read();
                     }
                     else
                     {
                         LogInformation(LogMessages.IDX30302, reader.LocalName, XmlEncryptionConstants.Elements.EncryptionMethod);
-                        reader.Skip();
                     }
+
+                    reader.Skip();
                 }
 
                 reader.ReadEndElement();

src/Microsoft.IdentityModel.Xml/KeyInfo.cs

@@ -291,6 +291,12 @@ internal void ReadXml(XmlDictionaryReader reader)
 
             if (reader.IsStartElement(XmlSignatureConstants.Elements.KeyInfo, XmlSignatureConstants.Namespace))
             {
+                if (reader.IsEmptyElement)
+                {
+                    reader.Skip();
+                    return;
+                }
+
                 reader.ReadStartElement(XmlSignatureConstants.Elements.KeyInfo, XmlSignatureConstants.Namespace);
 
                 while (reader.IsStartElement())