We want this software to be as widely available as possible, and still protect the freedom and integrity of it. In order to provide distribution through stores, as well as keep the software available under the GPL, we require any code contributions to come with a signed CLA.
It is normal for organizations to require a CLA for code contributions, for legal protection. See links below:
- Another well-written rationale: https://github.com/Medium/opensource/blob/master/cla-rationale.md
- Note from the Free Software Foundtaion: https://www.fsf.org/blogs/rms/assigning-copyright
Distribution in compiled form on stores in general can possibly be interpreted as violating the “Anti-Tivoization” clause of the GPL. This is because these apps are often cryptography signed, and refuse to execute if modified. Because we believe signing execution protects the integrity of the code for its intended use, and the end user in general, we grant a specific exemption to stores, at our discretion, to allow signing protection of the code in compiled form so long as it's from an unmodified, a publically avilable version of corresponding source code.
Places like the Apple Store licenses apps with added restrictions, such as being for use on a single device only. This is in conflict with the redistribution terms of the GPL. However, we believe that the availability of the app in these places is important. We grant a specific exemption to stores, at our discretion, to allow restriction of redistribution of a compiled form of the app, so long as it is cryptography signed to prevent execution if modified, and the compiled app makes a reference in a conspicuous place to a location where the full original source code that corresponds to it may be obtained.
We require code reference integrity. If at any point the reference back to the corresponding source in a compiled form of the code makes is no longer generally available, the app in complied form is no longer in compliance and must be removed from distribution. As an example, Our Voice USA publishes this code on its account on GitHub, and the store distributions refer back to it. If the code is removed from GitHub, or GitHub becomes no longer available to the public, the compiled apps that use that location as a reference will be removed and no longer be made available.
The intent of our CLA is to strike a balance in good faith between the purpose of the GPL license to protect the source code’s integrity and availability to the end user, so they can download and make modifications to it if they so desire, and making the app available to people through stores, many of who would otherwise be unable to use the software without it being available on the store. In order to do this, Our Voice USA needs to retain full copyright of the software so it can legally assign a different license for distribution through stores, and does so, so long as they meet all terms as described above.