From e67b25be77532af9ba405670b34b4d263d505fde Mon Sep 17 00:00:00 2001
From: msbw2 <brettwhite@microsoft.com>
Date: Mon, 22 Jul 2024 16:14:18 -0700
Subject: [PATCH] Fix string comparison with differing timestamps (#2739)

---
 .../IdentityComparer.cs                       | 37 +++++++++++++++++--
 .../IdentityComparerTests.cs                  | 10 +++++
 2 files changed, 43 insertions(+), 4 deletions(-)

diff --git a/test/Microsoft.IdentityModel.TestUtils/IdentityComparer.cs b/test/Microsoft.IdentityModel.TestUtils/IdentityComparer.cs
index 47b868d8a4..501275d644 100644
--- a/test/Microsoft.IdentityModel.TestUtils/IdentityComparer.cs
+++ b/test/Microsoft.IdentityModel.TestUtils/IdentityComparer.cs
@@ -19,6 +19,7 @@
 using System.Security.Cryptography;
 using System.Security.Cryptography.X509Certificates;
 using System.Text.Json;
+using System.Text.RegularExpressions;
 using Microsoft.IdentityModel.JsonWebTokens;
 using Microsoft.IdentityModel.Protocols;
 using Microsoft.IdentityModel.Protocols.OpenIdConnect;
@@ -1601,6 +1602,8 @@ public static bool AreStringsEqual(object object1, object object2, CompareContex
             return AreStringsEqual(object1, object2, "str1", "str2", context);
         }
 
+        private static readonly Regex timestampRegex = new Regex(@"\d{1,2}:\d{2}:\d{2}", RegexOptions.Compiled);
+
         public static bool AreStringsEqual(object object1, object object2, string name1, string name2, CompareContext context)
         {
             var localContext = new CompareContext(context);
@@ -1624,10 +1627,36 @@ public static bool AreStringsEqual(object object1, object object2, string name1,
 
             if (!string.Equals(str1, str2, context.StringComparison))
             {
-                localContext.Diffs.Add($"'{name1}' != '{name2}', StringComparison: '{context.StringComparison}'");
-                localContext.Diffs.Add($"'{str1}'");
-                localContext.Diffs.Add($"!=");
-                localContext.Diffs.Add($"'{str2}'");
+                // Try to find timestamps in the strings which might differ due to skew and compare them with epsilon.
+                MatchCollection match1 = timestampRegex.Matches(str1);
+                MatchCollection match2 = timestampRegex.Matches(str2);
+                int matched = 0;
+                // Check that at least one timestamp matched and both strings matched the same number of timestamps.
+                if (match1.Count != 0 && match1.Count == match2.Count)
+                {
+                    for (int i = 0; i < match1.Count; i++)
+                    {
+                        string time1 = match1[i].Value;
+                        string time2 = match2[i].Value;
+                        // If the matches match string-wise exactly or are parseable DateTimes and are equal within epsilon count as matched.
+                        if (time1 == time2 ||
+                            (DateTime.TryParse(time1, out DateTime datetime1) &&
+                            DateTime.TryParse(time2, out DateTime datetime2) &&
+                            AreDatesEqualWithEpsilon(datetime1, datetime2, 1)))
+                        {
+                            matched++;
+                        }
+                    }
+                }
+
+                // If no fancy timestamp comparison happened or some timestamps didn't match add the diff.
+                if (matched == 0 || matched != match1.Count)
+                {
+                    localContext.Diffs.Add($"'{name1}' != '{name2}', StringComparison: '{context.StringComparison}'");
+                    localContext.Diffs.Add($"'{str1}'");
+                    localContext.Diffs.Add($"!=");
+                    localContext.Diffs.Add($"'{str2}'");
+                }
             }
 
             return context.Merge(localContext);
diff --git a/test/Microsoft.IdentityModel.Tokens.Tests/IdentityComparerTests.cs b/test/Microsoft.IdentityModel.Tokens.Tests/IdentityComparerTests.cs
index ce17447c1c..15b0d16fb8 100644
--- a/test/Microsoft.IdentityModel.Tokens.Tests/IdentityComparerTests.cs
+++ b/test/Microsoft.IdentityModel.Tokens.Tests/IdentityComparerTests.cs
@@ -580,6 +580,16 @@ public void CompareStrings()
             Assert.True(context.Diffs[3] == $"'{string2}'");
         }
 
+        [Fact]
+        public void CompareStringsWithTimestamps()
+        {
+            TestUtilities.WriteHeader($"{this}.{nameof(CompareStringsWithTimestamps)}", true);
+            var context = new CompareContext($"{this}.{nameof(CompareStringsWithTimestamps)}");
+            DateTime now = DateTime.UtcNow;
+            IdentityComparer.AreEqual($"{now:HH:mm:ss} {now.AddSeconds(1):HH:mm:ss}", $"{now.AddSeconds(1):HH:mm:ss} {now:HH:mm:ss}", context);
+            Assert.Empty(context.Diffs);
+        }
+
         [Fact]
         public void CompareSymmetricSecurityKeys()
         {