CrmAzureKeyVaultExampleGetToken.cs

string clientId = "00000000-0000-0000-0000-000000000000";
string clientSecret = "00000000000000000000000000000000000000000000";
string tenantId = "00000000-0000-0000-0000-000000000000";

//Retrieve the access token required for authentication
var getTokenTask = Task.Run(async () => await GetToken(clientId, clientSecret, tenantId));
Task.WaitAll(getTokenTask);
if (getTokenTask.Result == null)
	throw new InvalidPluginExecutionException("Error retrieving access token");
//Deserialize the token response to get the access token
TokenResponse tokenResponse = DeserializeResponse<TokenResponse>(getTokenTask.Result);
string token = tokenResponse.access_token;

//Get the access token required to access the Key Vault
private async Task<string> GetToken(string clientId, string clientSecret, string tenantId)
{
	using (HttpClient httpClient = new HttpClient())
	{
		var formContent = new FormUrlEncodedContent(new[]
		{
			new KeyValuePair<string, string>("resource", "https://vault.azure.net"),
			new KeyValuePair<string, string>("client_id", clientId),
			new KeyValuePair<string, string>("client_secret", clientSecret),
			new KeyValuePair<string, string>("grant_type", "client_credentials")
		});

		HttpResponseMessage response = await httpClient.PostAsync(
			"https://login.windows.net/" + tenantId + "/oauth2/token", formContent);

		return !response.IsSuccessStatusCode ? null
			: response.Content.ReadAsStringAsync().Result;
	}
}

//Generic JSON to object deserialization 
private T DeserializeResponse<T>(string response)
{
	using (MemoryStream stream = new MemoryStream())
	{
		DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(T));
		StreamWriter writer = new StreamWriter(stream);
		writer.Write(response);
		writer.Flush();
		stream.Position = 0;
		T responseObject = (T)serializer.ReadObject(stream);
		return responseObject;
	}
}