/// <summary>
/// Uses a Refresh Token to obtain a new Access Token and stores it in the Token Manager.
/// </summary>
/// <returns>If successful, returns the new Access Token as a string. Otherwise...</returns>
///
private async Task <string> GetAndStoreApiAccessTokens()
{
TokenManager.ClearAccessTokens();
var disco = await GetDiscoveryDocumentAsync(_identityServerUrl);
var request = MakeAccountsApiRefreshTokenRequest(disco.TokenEndpoint,
TokenManager.GetAccessTokens().RefreshToken);
var response = await RequestRefreshTokenAsync(request);
// TODO: handle failure.
TokenManager.SetAccessTokens(response.AccessToken, response.RefreshToken);
return(response.AccessToken);
}