Get Office 365 using Microsoft Graph

GraphGetUserByIdentifier.cs

User user = null;
try
{
    user = await graphClient.Users[input].Request().GetAsync();
}
catch (ServiceException ex)
{
    if (ex.StatusCode == HttpStatusCode.NotFound)
        Console.WriteLine($"The user specified '{input}' is not a valid Office 365 user. Error message: {ex}");
    else
    {
        throw ex;
    }
}