/// <summary>
/// Refreshes an expired access token and updates the database.
/// </summary>
/// <param name="state">A user's app state.</param>
/// <param name="clientId">The client ID.</param>
/// <param name="oldAccessToken">The expired access token.</param>
/// <returns>The refreshed access token.</returns>
public async Task <string> RefreshAccessToken(Guid state, string clientId, string oldAccessToken)
{
string refreshToken, clientSecret;
// First, we have to get the refresh token
refreshToken = await authenticator.GetRefreshTokenByStateAsync(state);
// Next, we have to get the client secret
clientSecret = await authenticator.GetClientSecretByValidStateAsync(state);
// Okay, now let's make our POST request to Twitch
var refreshResponse = await twitchApi.Auth.v5.RefreshAuthTokenAsync(refreshToken, clientSecret, clientId);
await authenticator.UpdateAccessAndRefreshTokens(state, refreshResponse.AccessToken, refreshResponse.RefreshToken);
return(refreshResponse.AccessToken);
}