Windows, if using Windows, should remember the username and password when accessing a My Cloud device. Sometimes the Windows Credentials Manager will store the information. Windows generally doesn’t like mixed credentials, using more than one username/password when accessing an network attached storage device like the My Cloud.
You can have Windows auto login at startup to a mapped Share by selecting “reconnect at sign-in” when initially mapping the share through Windows File Explorer.
You could try creating an entry in the Windows Credential Manager for the My Cloud with the My Cloud Dashboard created user name and password and see if Windows will auto login when accessing the My Cloud.