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Remove closure from JsonWebTokenHandler.ValidateSignature #2169

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Jul 26, 2023
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Remove closure from JsonWebTokenHandler.ValidateSignature #2169

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3 changes: 2 additions & 1 deletion src/Microsoft.IdentityModel.JsonWebTokens/JsonWebTokenHandler.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1760,7 +1760,8 @@ private static JsonWebToken ValidateSignature(JsonWebToken jwtToken, TokenValida
{
if (kidMatched)
{
var isKidInTVP = keysInTokenValidationParameters.Any(x => x.KeyId.Equals(jwtToken.Kid));
JsonWebToken localJwtToken = jwtToken; // avoid closure on non-exceptional path
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This is so tricky to catch both when coding and in review. Is there a way a static analyzer could catch this? It would probably be super noisy.

I assume the best way to find these today is to look at the allocations in a trace?

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I assume the best way to find these today is to look at the allocations in a trace?

They certainly jump out at you there. "What is <>__DisplayClass_52 and why is it being allocated 18,000 times?"

In other projects, every now and then I'll also load up all the relevant assemblies in ILSpy, search for DisplayClass, and just flip through all of them to see whether they make sense.

Of course, the real solution is to avoid the patterns that lead to this in the first place, e.g. don't use Any(x => ...) and you won't close over anything, or use APIs that allow the TState to be passed in. And if you can avoid closing over stuff, protect it by using static on the lambda so they don't then regress.

var isKidInTVP = keysInTokenValidationParameters.Any(x => x.KeyId.Equals(localJwtToken.Kid));
var keyLocation = isKidInTVP ? "TokenValidationParameters" : "Configuration";
throw LogHelper.LogExceptionMessage(new SecurityTokenInvalidSignatureException(LogHelper.FormatInvariant(TokenLogMessages.IDX10511,
keysAttempted,
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