When Code Coverage Betrayed Me

I’m a fan of code coverage as a way to ensure that there are covering tests. One area that I tend to rely heavily on Code Coverage for is to catch any tests that are no longer working correctly due to changes in the production code. That often works out well, but today I got betrayed by the code coverage engine.

The code that I worked on contained an if statement with a multi-step && expression.

void IsAllWrong(int importantValue, bool b)
{
  bool a = importantValue == GetAnswer();
  bool c = false;
  bool d = false;
 
  if (!a && !b && !c && !d)
  {
    return true;
  }
  return false;
}

Of course I had tests that made the evaluation fail both because of importantValue and b. So what happend later was that GetAnswer() was updated, without the test for when importantValue being updated. Of course (my bad) that test had set b to true, causing the evaluation to fail on b, causing true to be returned. So the test passed, but not due to the thing I wanted to test. In a complex application, this is bound to happen every now and then. But usually, the code coverage scores will reveal that there is an execution path not covered. But not this time! The trustworthy code coverage analysis betrayed me!

Kentor.AuthServices v0.20.0 Released

Half a years worth of pull requests with great features have finally been baked into an official release of Kentor.AuthServices which is now available on Nuget. The most important fixes are improved active/passive handling for the Owin middleware and full support for SHA256/384/512 as it is time to leave SHA1.

First of all I would like thank all contributors and users that have had to wait for this while I’ve been on parental leave. A special thanks to Explunit who has made a lot of valuable contributions as well as reviewing pull requests and taken part in design discussions.

Breaking Changes

The public API of AuthServices is getting more and more stable, but nevertheless there are some breaking changes.

  • The Owin Middleware is now once again Passive by default
  • The Owin Middleware will act as Active during Logout, even if it is configured as passive. This can be disabled with the StrictOwinAuthenticationMode compatibility setting.
  • On .NET 4.6.2 and later AuthServices now by default generates SHA256-based signatures and only accepts SHA256 or stronger signatures.
  • The “clever” ReturnUrl expansion has been removed as it proved to create more problems than it solved.
  • ReturnUrl open redirect issue fixed.

Why Enabling SHA256 Support for XML Signatures Breaks JWT Signing

For some times there’s been bug reports to Kentor.AuthServices, IdentityServer3 and System.IdentityModel.Tokens.Jwt about enabling SHA256 XML signature support sometimes breaks JWT signing. It fails with an error of System.Security.Cryptography.CryptographicException: Invalid algorithm specified.

This has been one of those annoying bugs where everyone’s solution works perfectly by itself, but combined they fail. I closed this issue in AuthServices with a comment that “works for us, has to be IdentityServer3/System.IdentityModel.Tokens doing something strange.”. I’ve finally had some time to look deeper into this thanks to IRM that asked me to do this as a consultancy service. Without someone paying for the time, it’s hard to spend the hours needed to find the root cause of a problem like this. When I started out on this I looked at all three systems/components involved to try to understand what triggers the problem. I ended up fixing this in Kentor.AuthServices for now. The fix could also have been done in the .NET Framework, IdentityServer3 or System.IdentityModel.Tokens.Jwt. Doing it in Kentor.AuthServices was mostly a matter of convenience because I control it myself.

That means that the TL;DR of all of this is that if you update to Kentor.AuthServices 0.19.0 or later this problem is solved. If you’re interested on how to solve it if you add SHA256 support yourself, please read on.

String Split and Join with Escaping

.NET offers the simple string.Split() and string.Join() methods for joining and splitting separated strings. But what if there is no suitable separator character that may not occur in the string? Then the separator character must be escaped. And then the escape character must be escaped too… And this turns out to be quite an interesting algorithm to write.

I thought that this functionality would be built in, but as far as I could find out it isn’t. If there is a built in way, please leave a comment to educate me. This being a string manipulation, there is a possibility to use Regular Expressions too, but…

Some people, when confronted with a problem, think “I know, I’ll use regular expressions.” Now they have two problems.

Jamie Zawinski

Solving this through a Regular Expression would require some black magic double look-behind assertion which I wouldn’t understand even when I wrote the code, much less later when I came back to fix some bug. So I went for implementing it myself.

Breaking Changes to SignedXml in MS16-035

xml-ms16-035Earlier this month, Microsoft released MS16-035 that addresses issues I previously reported in SignedXml. They did not only fix the duplicate Id vulnerability I reported though, they also fixed a number of other issues – introducing some breaking changes. This post is an effort to document those and changes and the registry switches that can be used to revert back to the old behaviour.

These are the breaking changes I know about. If you know of any more issues, please leave a comment or drop a mail and I’ll try to update the post.

  1. Duplicate Ids for reference elements no longer allowed (applies to both SignedXml and EncryptedXml)
  2. Id values must be a well formed NCName (which is required by the XML standard, applies to both SignedXml and EncryptedXml)
  3. External references disabled by default
  4. XPath Transform disabled by default
  5. XSLT Transform disabled by default
Software Development is a Job – Coding is a Passion

I'm Anders Abel, a systems architect and developer working for Kentor in Stockholm, Sweden.

profile for Anders Abel at Stack Overflow, Q&A for professional and enthusiast programmers

Code for most posts is available on my GitHub account.

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