Fix XML Equality Check by Comparing Parsed XML Structure Instead of Raw Strings

test/Microsoft.IdentityModel.TestUtils/IdentityComparer.cs

@@ -20,6 +20,7 @@
 using System.Security.Cryptography.X509Certificates;
 using System.Text.Json;
 using System.Text.RegularExpressions;
+using System.Xml.Linq;
 using Microsoft.IdentityModel.JsonWebTokens;
 using Microsoft.IdentityModel.Protocols;
 using Microsoft.IdentityModel.Protocols.OpenIdConnect;
@@ -143,6 +144,7 @@ public class IdentityComparer
                 { typeof(SignedInfo).ToString(), CompareAllPublicProperties },
                 { typeof(SigningCredentials).ToString(), CompareAllPublicProperties },
                 { typeof(string).ToString(), AreStringsEqual },
+                { typeof(XDocument).ToString(), AreXmlsEqual },
                 { typeof(SymmetricSecurityKey).ToString(), CompareAllPublicProperties },
                 { typeof(TimeSpan).ToString(), AreTimeSpansEqual },
                 { typeof(TokenValidationParameters).ToString(), CompareAllPublicProperties },
@@ -1171,6 +1173,147 @@ public static bool AreStringDictionariesEqual(Object object1, Object object2, Co
             context.Diffs.AddRange(localContext.Diffs);
             return localContext.Diffs.Count == 0;
         }
+        public static bool AreXmlsEqual(object xml1, object xml2, CompareContext context)
+        {
+            try
+            {
+                return AreXmlsEqual((XDocument)xml1, (XDocument)xml2, "xml1", "xml2", context);
+            }
+            catch (InvalidCastException ex)
+            {
+                context.Diffs.Add($"unable to cast {xml1.ToString()} and/or {xml2.ToString()} to xml document. Exception: '{ex}'.");
+                return false;
+            }
+        }
+
+        private static bool AreXmlsEqual(XDocument xml1, XDocument xml2, string name1, string name2, CompareContext context)
+        {
+            var localContext = new CompareContext(context);
+            if (!ContinueCheckingEquality(xml1, xml2, localContext))
+                return context.Merge(localContext);
+
+            if (ReferenceEquals(xml1, xml2))
+                return true;
+
+            if (!CompareXmlElements(xml1.Root, xml2.Root, localContext))
+            {
+                localContext.Diffs.Add($"'{name1}' != '{name2}', StringComparison: '{context.StringComparison}'");
+                localContext.Diffs.Add($"'{xml1.ToString()}'");
+                localContext.Diffs.Add($"!=");
+                localContext.Diffs.Add($"'{xml2.ToString()}'");
+            }
+
+            return context.Merge(localContext);
+        }
+
+        /// <summary>
+        /// Compares two XML elements for equality, ignoring order of attributes and child elements.
+        /// Ignore X509 certificate elements and attributes.
+        /// </summary>
+        /// <param name="elem1">The first XML element to compare.</param>
+        /// <param name="elem2">The second XML element to compare.</param>
+        /// <param name="localContext"></param>
+        /// <returns>True if the elements are considered equal, otherwise false.</returns>
+        private static bool CompareXmlElements(XElement elem1, XElement elem2, CompareContext localContext)
+        {
+            // Ensure both elements exist; if one is null while the other isn't, they are not equal.
+            if (elem1 == null || elem2 == null)
+            {
+                localContext.Diffs.Add($"one of the xml elements is null");
+                localContext.Diffs.Add($"'{elem1.ToString()}'");
+                localContext.Diffs.Add($"!=");
+                localContext.Diffs.Add($"'{elem2.ToString()}'");
+                return false;
+            }
+
+            // Compare element names; if they are different, the elements are not equal.
+            if (elem1.Name != elem2.Name)
+            {
+                localContext.Diffs.Add($"xml element names are not equal, StringComparison: '{localContext.StringComparison}'");
+                localContext.Diffs.Add($"'{elem1.Name.ToString()}'");
+                localContext.Diffs.Add($"!=");
+                localContext.Diffs.Add($"'{elem2.Name.ToString()}'");
+                return false;
+            }
+
+            // Ignore comparison for elements related to X509 certificates.
+            if (elem1.Name.ToString().Contains("X509"))
+                return true;
+
+            // Retrieve and order attributes by name to ensure order-independent comparison.
+            var attrs1 = elem1.Attributes().OrderBy(a => a.Name.ToString()).ToList();
+            var attrs2 = elem2.Attributes().OrderBy(a => a.Name.ToString()).ToList();
+
+            // If the number of attributes differs, the elements are not equal.
+            if (attrs1.Count != attrs2.Count)
+            {
+                localContext.Diffs.Add($"number of xml element attributes are not the same");
+                localContext.Diffs.Add($"'{attrs1.Count}'");
+                localContext.Diffs.Add($"!=");
+                localContext.Diffs.Add($"'{attrs2.Count}'");
+                return false;
+            }
+
+            // Compare attributes
+            for (int i = 0; i < attrs1.Count; i++)
+            {
+                // Compare attribute names; if different, the elements are not equal.
+                if (attrs1[i].Name != attrs2[i].Name)
+                {
+                    localContext.Diffs.Add($"the xml element attribute names are not equal, StringComparison: '{localContext.StringComparison}'");
+                    localContext.Diffs.Add($"'{attrs1[i].Name}'");
+                    localContext.Diffs.Add($"!=");
+                    localContext.Diffs.Add($"'{attrs2[i].Name}'");
+                    return false;
+                }
+
+                // Ignore attributes related to X509 certificates.
+                if (attrs1[i].Name.ToString().Contains("X509"))
+                    continue;
+
+                // Compare attribute values using the specified string comparison method.
+                if (!string.Equals(attrs1[i].Value, attrs2[i].Value, localContext.StringComparison))
+                {
+                    localContext.Diffs.Add($"the xml element attribute values are not equal, StringComparison: '{localContext.StringComparison}'");
+                    localContext.Diffs.Add($"'{attrs1[i].Value}'");
+                    localContext.Diffs.Add($"!=");
+                    localContext.Diffs.Add($"'{attrs2[i].Value}'");
+                    return false;
+                }
+            }
+
+            // Retrieve and order child elements by name to ensure order-independent comparison.
+            var children1 = elem1.Elements().OrderBy(e => e.Name.ToString()).ToList();
+            var children2 = elem2.Elements().OrderBy(e => e.Name.ToString()).ToList();
+
+            // If the number of child elements differs, the elements are not equal.
+            if (children1.Count != children2.Count)
+            {
+                localContext.Diffs.Add($"number of xml element childrens are not the same");
+                localContext.Diffs.Add($"'{children1.Count}'");
+                localContext.Diffs.Add($"!=");
+                localContext.Diffs.Add($"'{children2.Count}'");
+                return false;
+            }
+
+            // Recursively compare child elements.
+            for (int i = 0; i < children1.Count; i++)
+            {
+                if (!CompareXmlElements(children1[i], children2[i], localContext))
+                    return false; // Child elements mismatch
+            }
+
+            // If the element has no children, compare its values.
+            if (children1.Count == 0 && !string.Equals(elem1.Value.Trim(), elem2.Value.Trim(), localContext.StringComparison))
+            {
+                localContext.Diffs.Add($"the xml element value are not equal, StringComparison: '{localContext.StringComparison}'");
+                localContext.Diffs.Add(elem1.Value.Trim());
+                localContext.Diffs.Add("!=");
+                localContext.Diffs.Add(elem2.Value.Trim());
+                return false;
+            }
+            return true;
+        }
 
         public static bool AreStringsEqual(object object1, object object2, CompareContext context)
         {

test/Microsoft.IdentityModel.Xml.Tests/DSigSerializerTests.cs

@@ -7,6 +7,7 @@
 using System.Security.Cryptography;
 using System.Text;
 using System.Xml;
+using System.Xml.Linq;
 using Microsoft.IdentityModel.TestUtils;
 using Microsoft.IdentityModel.Tokens;
 using Xunit;
@@ -114,7 +115,21 @@ public void WriteKeyInfo(DSigSerializerTheoryData theoryData)
                 theoryData.Serializer.WriteKeyInfo(writer, keyInfo);
                 writer.Flush();
                 var xml = Encoding.UTF8.GetString(ms.ToArray());
-                IdentityComparer.AreEqual(theoryData.Xml, xml);
+
+                // Compare the original XML with the re-serialized XML.
+                // Parsing the XML strings into XDocument ensures that the comparison is based on 
+                // structural and content equality rather than raw string differences (formatting, whitespace,...).
+                IdentityComparer.AreEqual(XDocument.Parse(theoryData.Xml), XDocument.Parse(xml), context);
+            }
+            catch (InvalidCastException ex)
+            {
+                context.Diffs.Add($"InvalidCastException: {ex.Message}");
+                theoryData.ExpectedException.ProcessException(ex, context.Diffs);
+            }
+            catch (XmlException ex)
+            {
+                context.Diffs.Add($"XmlException: {ex.Message}");
+                theoryData.ExpectedException.ProcessException(ex, context.Diffs);
             }
             catch (Exception ex)
             {