Fix timezone issue in dev-certs: use DateTimeOffset.UtcNow instead of DateTimeOffset.Now

src/Tools/FirstRunCertGenerator/src/CertificateGenerator.cs

@@ -11,7 +11,7 @@ public static class CertificateGenerator
     public static void GenerateAspNetHttpsCertificate()
     {
         var manager = CertificateManager.Instance;
-        var now = DateTimeOffset.Now;
+        var now = DateTimeOffset.UtcNow;
         manager.EnsureAspNetCoreHttpsDevelopmentCertificate(now, now.AddYears(1), isInteractive: false);
     }
 }

src/Tools/FirstRunCertGenerator/test/CertificateManagerTests.cs

@@ -516,6 +516,40 @@ public void ListCertificates_AlwaysReturnsTheCertificate_WithHighestVersion()
                 e.RawData[0] == 2);
     }
 
+    [Fact]
+    public void CreateAspNetCoreHttpsDevelopmentCertificate_UsesUtcTime_NotLocalTime()
+    {
+        // This test verifies that the certificate NotBefore time is based on UTC, not local timezone
+        // This prevents issues where certificates appear "not yet valid" in different timezones
+
+        try
+        {
+            _fixture.CleanupCertificates();
+
+            // Use a known UTC time as the basis for the certificate
+            var utcNow = new DateTimeOffset(2024, 1, 15, 12, 0, 0, TimeSpan.Zero); // UTC noon
+            var utcExpiry = utcNow.AddYears(1);
+
+            // Create certificate with UTC-based times
+            var certificate = _manager.CreateAspNetCoreHttpsDevelopmentCertificate(utcNow, utcExpiry);
+
+            // Verify that NotBefore matches the UTC time we provided, not a local time
+            // The certificate should be immediately valid at the specified UTC time
+            var expectedNotBefore = utcNow.UtcDateTime;
+            var actualNotBefore = certificate.NotBefore.ToUniversalTime();
+
+            // Allow for some minor timing differences (within 1 second)
+            var timeDifference = Math.Abs((expectedNotBefore - actualNotBefore).TotalSeconds);
+            Assert.True(timeDifference < 1, 
+                $"Certificate NotBefore should match UTC time. Expected: {expectedNotBefore:yyyy-MM-dd HH:mm:ss} UTC, " +
+                $"Actual: {actualNotBefore:yyyy-MM-dd HH:mm:ss} UTC, Difference: {timeDifference:F2} seconds");
+        }
+        finally
+        {
+            _fixture.CleanupCertificates();
+        }
+    }
+
     [ConditionalFact]
     [OSSkipCondition(OperatingSystems.Windows, SkipReason = "UnixFileMode is not supported on Windows.")]
     [OSSkipCondition(OperatingSystems.MacOSX, SkipReason = "https://github.com/dotnet/aspnetcore/issues/6720")]

src/Tools/dotnet-dev-certs/src/Program.cs

@@ -371,7 +371,7 @@ private static int CheckHttpsCertificateJsonOutput(IReporter reporter)
 
     private static int EnsureHttpsCertificate(CommandOption exportPath, CommandOption password, CommandOption noPassword, CommandOption trust, CommandOption exportFormat, IReporter reporter)
     {
-        var now = DateTimeOffset.Now;
+        var now = DateTimeOffset.UtcNow;
         var manager = CertificateManager.Instance;
 
         if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))