private async Task RefreshCredentialsAsync(GoogleCredentials credentials)
{
var clientId = apiKeyRepository.GetClientId();
var clientSecret = apiKeyRepository.GetClientSecret();
var url = new StringBuilder();
url.Append("https://oauth2.googleapis.com/token?");
url.Append($"client_id={clientId}&");
url.Append($"client_secret={clientSecret}&");
url.Append($"refresh_token={UrlEncode(credentials.RefreshToken)}&");
url.Append($"grant_type=refresh_token");
var responseMessage = await httpClient.PostAsync(url.ToString(), null);
responseMessage.EnsureSuccessStatusCode();
var response = JsonConvert.DeserializeObject <JObject>(
await responseMessage.Content.ReadAsStringAsync()
);
var accessToken = response.Value <string>("access_token");
var expirySeconds = response.Value <int>("expires_in");
var expiry = DateTime.Now + TimeSpan.FromSeconds(expirySeconds - 5);
credentials.AccessToken = accessToken;
credentials.AccessTokenExpiry = expiry;
}