Unity

<?xml version="1.0" encoding="utf-8"?>
<!-- Assets/packages.config, after installing NuGetForUnity: it restores Lingara.Embed and places each platform's native library. -->
<packages>
  <package id="Lingara.Embed" version="0.1.0-alpha.6" manuallyInstalled="true" />
</packages>

[Serializable]
private struct Handoff { public string token; public string expires_at; }

// Your own server mints the token: never put a client secret in a game.
private IEnumerator FetchToken()
{
    using (var request = UnityWebRequest.PostWwwForm(tokenUrl, string.Empty))
    {
        yield return request.SendWebRequest();
        if (Client == null) yield break;
        if (request.result != UnityWebRequest.Result.Success)
        {
            Client.TokenUnavailable(request.error); // fail the waiting calls now
            yield break;
        }
        var handoff = JsonUtility.FromJson<Handoff>(request.downloadHandler.text);
        Client.ProvideToken(handoff.token, handoff.expires_at);
    }
}

private void Update()
{
    if (Client == null) return;
    events.Clear();
    Client.Drain(events); // at most 256 a frame; the rest wait for the next
    foreach (var e in events)
    {
        switch (e)
        {
            case EmbedEvent.TokenNeeded _: StartCoroutine(FetchToken()); break;
            case EmbedEvent.NpcTurn turn: NpcTurn?.Invoke(turn); break;
            case EmbedEvent.Practice practice: Practice?.Invoke(practice); break;
            case EmbedEvent.LingaraReceived received: LingaraReceived?.Invoke(received); break;
            case EmbedEvent.Failed failed: Failed?.Invoke(failed); break;
            case EmbedEvent.Log log: Debug.Log($"[lingara] {log.Level} {log.Target}: {log.Message}"); break;
        }
    }
}