The LGPL License

TL;DR A component licensed under LGPL can be used by closed source, proprietary software, both internally used and distributed, for free, with no effects on the software using the component. LGPL is not “contagious” in the same way as GPL, so it only affects the component under LGPL. As long as you’re only using official distributions of the component, it is free to use and free to redistribute. The only requirement is that you include a notice in your “about” page or similar that the component is used.

I often get questions about the LGPL license used for Kentor.AuthServices. I also often find it confused with GPL, which is something you should never, ever even consider to use in any closed source software that you intend to distribute. So this post is an effort to explain and answer common questions about the LGPL. Unfortunately I have to add the disclaimer: I’m not a lawyer and the content of this post is only meant as an overview and introduction to the license. I might have got things wrong, so please read the real license yourself and involve appropriate legal counsel to be sure.

I’m a Microsoft MVP

I’m grateful, humbled and proud to receive the Microsoft MVP Award.

mvpEver since I first heard of the MVP program nearly 15 years ago I’ve had a great respect for those receiving the award. The MVPs I’ve met and got to know have all possessed that rare combination of deep technical knowledge and the social skills needed to communicated them. I’ve read blog posts, attended talks, watched videos, used open source and read open source by MVPs and learnt so much from them. And now I’m also an MVP. As much as I’m grateful and proud I’m also humbled (and a bit horrified) about being invited to be one of them.

Thanks for giving me the chance, now it’s up to me to prove that I’m worthy of a renewal next year.

Posted in Other on 2016-10-22

Static Analysis with NDepend

Static Analysis has interested me for nearly as long as I’ve been coding, so when I was offered to try out NDepend I got really excited. I already rely on the warnings the compiler can give and code analysis rules for my projects and a tool such as NDepend seems like the next logical step. I was not disappointed.

I think that the code analysis rules offered by Visual Studio are powerful and helps improve code quality, but they have a user experience that’s more punishing than encouraging. Code Analysis rules are evaluated after the code is written and after it has passed the compilation – which means when you are sort of done. Then it comes and tells you that you’re not done. That’s demoralising. There’s also no hint of how many rules you did in fact dit pass. The NDepend analysis is different. It is run from the NDepend Dashboard and it shows not just rules violations, but it can also show that your code is good.

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.

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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