Licensing NuGet packages per developer

Question

I am creating a product that is distributed via a NuGet package. I'm wondering if there is a way to identify the person who is compiling a project using my assemblies. I need this information for licensing purposes. Is it possible to check if a specific developer is compiling the project in Visual Studio?

Answer 1

Is it possible to check if a specific developer is compiling the project in Visual Studio?

Not natively.

You would typically to implement a licensing server, where developers must register to obtain a license key (a bit like Google did with its Xamarin.Google.Android.Vending.Licensing). That server can issue license keys tied to specific developer identifiers (e.g., email addresses).
You could also modify your NuGet package to require a license key as part of its initialization process. That key would be checked either locally against a simple encryption/validation scheme or remotely by contacting the licensing server.

A Visual Studio extension would help in obtaining and managing license keys for your package. That extension can guide the developer through the process of registering and inserting the required license key into their project.
If you want to add some form of compile-time validation, consider using MSBuild tasks or targets. You can include a custom MSBuild task in your NuGet package that runs during the build process, verifying the presence and validity of a license key.

<!-- Example of an MSBuild target in your NuGet package -->
<Target Name="CheckLicense" BeforeTargets="BeforeBuild">
  <Exec Command="dotnet your-package-license-check.dll --licenseKey $(LicenseKey)" />
</Target>

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It's unclear how to get the email of a developer who compiles the project with my assembly.

True: directly obtaining the email of a developer who compiles a project with your assembly is not feasible due to privacy and security reasons. The compilation process does not expose personal information about the developer, and Visual Studio does not provide a built-in mechanism to capture such details during compilation.

Instead, the licensing mechanism you employ should be designed to associate a license key with a developer's email or identifier through a registration process, rather than trying to capture this information at compile time.

It would involve the following steps:

1. Registration: require developers to register on your licensing server or portal. During this process, they provide their email and any other required details. In return, they receive a unique license key.

2. License Key Activation: Once the developer has the license key, they need to activate it within their development environment. That activation process can be manual (e.g., entering the key into a configuration file or through a GUI in a Visual Studio extension) or automated in some aspects.

3. Verification: When the developer compiles a project that includes your NuGet package, the package can check for a valid license key. That check can be:

   • Local: Verifying the key's format or using a simple encryption/validation scheme.
   • Remote: Sending the key to your server for validation. That method can log the key usage and perform more sophisticated checks but requires an internet connection.

For the compile-time check, your MSBuild task or target does not directly capture the developer's email. Instead, it verifies the presence and validity of a pre-registered and activated license key within the project:

<!-- Example of an MSBuild target in your NuGet package -->
<Target Name="CheckLicense" BeforeTargets="BeforeBuild">
  <Exec Command="dotnet your-package-license-check.dll --licenseKey $(LicenseKey)" />
</Target>

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The main issue, for now, is knowing that a specific developer uses the tool and didn't pass the license key to anyone else

So the main issue is making sure that a license key issued to a specific developer is used solely by that individual, rather than being shared or distributed.

There is no system entirely foolproof, but you could use one of those approaches (or combine them) to make it more difficult for a license key to be shared or used by multiple developers:

• Machine binding: Bind the license key to specific machine characteristics (e.g., MAC address, hard drive serial number, etc.). That does not identify the developer directly but ensures the key is used on registered machines only.

• License Key activation with limited seats: Implement a licensing model where a key has a limited number of "seats" or activations. Each activation is tied to a machine or development environment. The developer must manage activations within their allotted seats, making it less likely for the key to be shared widely without detection.

• Usage analytics: Incorporate usage analytics into your package, with the consent of the users. That can include anonymized data points such as frequency of use, types of projects it is being used on, and general geographic location (e.g., IP geolocation). Over time, patterns may emerge that suggest whether a key is being used by multiple developers.

• Regular license validation: Regularly validate license keys against the server, and include a check for the number of concurrent uses. If a key is being used by multiple developers simultaneously in a way that suggests sharing (e.g., being used in different geographic locations within a short timeframe), this could flag the license for review.

• Developer identification through registration process: While you cannot capture the developer's identity at compile time, you can require that the developer provides identifiable information during the registration process for a license key. That does not prevent key sharing but establishes a legal and ethical expectation of use.