Verify licenses in .NET

Reference MyApp.Licensing/MyApp.Licensing.csproj from your .NET 10 application. LicenseJwt uses the runtime's built-in P-256 cryptography and JSON support, and never contacts a server.

using MyApp.Licensing;

// Public key, issuer, product and build date come from your app, never from user input.
var result = LicenseJwt.Verify(
    pastedKey,
    embeddedPublicKeyPem,
    issuer: "acme-studio",
    product: "acme-studio",
    buildDate: "2026-09-21");

bool enablePro = result.Valid;
if (result.License is { } license)
{
    Console.WriteLine($"Registered to {license.Name}");
    Console.WriteLine($"Organization: {license.Organization}");
    Console.WriteLine($"Licensed seats: {license.Seats}");
}

Embed the public key and build date

Set both at build time so neither can be supplied through the license import form. MyApp.SampleApp.csproj shows one way to do it:

<PropertyGroup>
  <AppBuildDate Condition="'$(AppBuildDate)' == ''">2026-09-21</AppBuildDate>
</PropertyGroup>
<ItemGroup>
  <AssemblyMetadata Include="BuildDate" Value="$(AppBuildDate)" />
</ItemGroup>
<ItemGroup Condition="'$(LicensePublicKeyFile)' != ''">
  <EmbeddedResource Include="$(LicensePublicKeyFile)" LogicalName="Acme.LicensePublicKey" />
</ItemGroup>

At runtime, read the date from the BuildDate assembly metadata attribute and the key from the Acme.LicensePublicKey manifest resource. The sample also fails dotnet publish when no public key file is supplied, so a demo key can't ship by accident.

Use the result in your app

Bind menu and button availability to result.Valid, and check the same result inside the operation itself so keyboard shortcuts and scripts follow the same rule:

string ExportPro(string text, LicenseCheck license)
{
    if (!license.Valid)
        throw new InvalidOperationException("A license for this version is required.");
    return "PRO EXPORT\n" + text;
}

Save the license key itself as a local user file or preference and verify it again on each startup. Never persist only an isPro flag. If importing a replacement key fails, keep the previous valid one.

result.Status tells you what to show:

result.License is populated for valid, buildNotCovered and editionNotCovered, so an uncovered license can still show a friendly "Registered to … — renew to use this version" message. It is null for missing and invalid; never display unverified payload data. A wrong signature, issuer or product, or a malformed token, returns invalid. A malformed buildDate is an app configuration bug and throws.

There is no DateTime.UtcNow check anywhere: covered builds keep working forever, and network failures can't change the result.

Run and publish the sample

dotnet run --project MyApp.SampleApp
dotnet run --project MyApp.SampleApp -- --desktop

dotnet publish MyApp.SampleApp -c Release -r win-x64 --self-contained true \
  -p:LicensePublicKeyFile=/absolute/path/license-public.pem \
  -p:AppBuildDate=2026-09-21

Without an embedded key, the sample generates a disposable key and example covered, uncovered and Lifetime licenses. The desktop window demonstrates Free editing, Pro export/uppercase and registered details.

Other target frameworks

MyApp.Licensing targets .NET 10. For older frameworks, or other languages, use any maintained ES256-capable JWT library and apply the same checks; see standard JWT compatibility.