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Fix DateTime claim value type recognition for ISO8601 strings with and without trailing zeros #3373

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Fix DateTime claim value type recognition for ISO8601 strings with and without trailing zeros #3373

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6 changes: 2 additions & 4 deletions src/Microsoft.IdentityModel.JsonWebTokens/JwtTokenUtilities.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -619,11 +619,9 @@ internal static string GetStringClaimValueType(string str, string claimType)
if (!string.IsNullOrEmpty(claimType) && !AppContextSwitches.TryAllStringClaimsAsDateTime && JsonSerializerPrimitives.IsKnownToNotBeDateTime(claimType))
return ClaimValueTypes.String;

if (DateTime.TryParse(str, out DateTime dateTimeValue))
if (DateTime.TryParse(str, null, DateTimeStyles.AdjustToUniversal | DateTimeStyles.AssumeUniversal, out _))
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Copilot AI Dec 3, 2025

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The change to use DateTimeStyles.AdjustToUniversal | DateTimeStyles.AssumeUniversal is broader than just handling trailing zeros. This will now classify ANY parseable DateTime string as a DateTime claim, including:

  • Date-only strings like "2019-11-15" (previously String, now DateTime)
  • Ambiguous formats like "01/02/2023"
  • Relative date strings that DateTime.TryParse might accept

This is a significant behavioral change beyond the trailing zeros issue described in the PR. Consider:

  1. Adding comprehensive tests for various date formats to document the new behavior
  2. Verifying this doesn't break existing applications that expect certain date strings to remain as String type
  3. Evaluating if DateTimeStyles.RoundtripKind (used in JsonSerializerPrimitives.cs line 151) would be more appropriate to maintain consistency and only accept ISO8601 roundtrip formats
Suggested change
if (DateTime.TryParse(str, null, DateTimeStyles.AdjustToUniversal | DateTimeStyles.AssumeUniversal, out _))
if (DateTime.TryParseExact(str, "O", CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind, out _))

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{
string dtUniversal = dateTimeValue.ToUniversalTime().ToString("o", CultureInfo.InvariantCulture);
if (dtUniversal.Equals(str, StringComparison.Ordinal))
return ClaimValueTypes.DateTime;
return ClaimValueTypes.DateTime;
}

return ClaimValueTypes.String;
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16 changes: 16 additions & 0 deletions test/Microsoft.IdentityModel.JsonWebTokens.Tests/JwtTokenUtilitiesTests.cs
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Expand Up @@ -8,6 +8,7 @@
using System.IO;
using System.Linq;
using System.Reflection;
using System.Security.Claims;
using System.Text;
using Microsoft.IdentityModel.Logging;
using Microsoft.IdentityModel.Protocols.OpenIdConnect;
Expand Down Expand Up @@ -218,6 +219,21 @@ public void ResolveTokenSigningKey()
Assert.Null(resolvedKey);
}

#region GetStringClaimValueType

[Fact]
public void GetStringClaimValueType_ReturnsDateTime_ForIso8601WithOrWithoutTrailingZeros()
{
var iso8601WithTrailingZeros = "2025-11-26T09:30:45.1234560Z";
var iso8601WithoutTrailingZeros = "2025-11-26T09:30:45.123456Z";
var resultWithTrailingZeros = JwtTokenUtilities.GetStringClaimValueType(iso8601WithTrailingZeros);
var resultWithoutTrailingZeros = JwtTokenUtilities.GetStringClaimValueType(iso8601WithoutTrailingZeros);
Assert.Equal(ClaimValueTypes.DateTime, resultWithTrailingZeros);
Assert.Equal(ClaimValueTypes.DateTime, resultWithoutTrailingZeros);
}
Comment on lines +224 to +233
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Copilot AI Dec 3, 2025

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Consider adding test cases for edge cases beyond trailing zeros, such as:

  • Date-only strings: "2019-11-15"
  • Various ISO8601 formats: "2019-11-15T14:31:21Z", "2019-11-15T14:31:21+00:00"
  • Non-ISO8601 formats that DateTime.TryParse accepts: "11/15/2019", "Nov 15, 2019"
  • Strings that should remain as String type

This would document the new behavior comprehensively and ensure the change works as intended across different scenarios.

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#endregion

#region DecryptJwtToken Tests
[Fact]
public void DecryptJwtToken_WhenValidationParametersIsNull_ThrowsException()
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18 changes: 18 additions & 0 deletions test/System.IdentityModel.Tokens.Jwt.Tests/JwtPayloadTest.cs
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Expand Up @@ -7,6 +7,7 @@
using System.Reflection;
using System.Security.Claims;
using System.Text;
using Microsoft.IdentityModel.JsonWebTokens;
using Microsoft.IdentityModel.TestUtils;
using Microsoft.IdentityModel.Tokens;
using Microsoft.IdentityModel.Tokens.Json;
Expand Down Expand Up @@ -182,6 +183,23 @@ public void TestDateTimeClaim()
Assert.True(string.Equals(dateTimeClaim.Value, dateTime.ToUniversalTime().ToString("o", CultureInfo.InvariantCulture)), "dateTimeClaim.Value != dateTime.ToUniversalTime('o', CultureInfo.InvariantCulture).ToString()");
}

[Fact]
public void TestReturnsDateTime_ForIso8601WithOrWithoutTrailingZeros()
{
var iso8601WithTrailingZeros = "2025-11-26T09:30:45.1234560Z";
var iso8601WithoutTrailingZeros = "2025-11-26T09:30:45.123456Z";
var jwtpayload = new JwtPayload
{
{ "dateWithTrailingZeros", iso8601WithTrailingZeros },
{ "dateWithoutTrailingZeros", iso8601WithoutTrailingZeros }
};

var claimWithTrailingZeros = jwtpayload.Claims.First(c => c.Type == "dateWithTrailingZeros");
var claimWithoutTrailingZeros = jwtpayload.Claims.First(c => c.Type == "dateWithoutTrailingZeros");
Assert.Equal(ClaimValueTypes.DateTime, claimWithTrailingZeros.ValueType);
Assert.Equal(ClaimValueTypes.DateTime, claimWithoutTrailingZeros.ValueType);
}
Comment on lines +186 to +201
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Copilot AI Dec 3, 2025

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Consider adding test cases for edge cases beyond trailing zeros, such as:

  • Date-only strings: "2019-11-15"
  • Various ISO8601 formats with different timezone indicators
  • Non-ISO8601 formats that DateTime.TryParse accepts
  • Strings that should remain as String type

This would document the new behavior comprehensively and ensure the change works as intended across different scenarios.

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[Fact]
public void TestClaimWithLargeExpValue()
{
Expand Down