1. 环境配置：
   https://docs.microsoft.com/zh-cn/sharepoint/dev/sp-add-ins/using-csom-for-dotnet-standard

2. CSOM 基本的API：
   https://docs.microsoft.com/zh-cn/sharepoint/dev/sp-add-ins/complete-basic-operations-using-sharepoint-client-library-code

补充：
String 和SecureString 的转换：
String to SecureString： SecureString theSecureString = new NetworkCredential("", "myPass").SecurePassword;
SecureString to String： string theString = new NetworkCredential("", theSecureString).Password;