I am using web url in my dashboard. When I choose Authentication method Windows, I don't see it asks for any username or password. If Windows authentication doesn't require any credentials, then what username and password does it sent to the URL.
When choosing Windows authentication method, it uses the account that you use to log in the current computer and the credential of this log-on account. For more details about Windows authentication, please review this article: https://technet.microsoft.com/en-us/library/hh831472(v=ws.11).aspx .
In addition, which authentication method do you choose when connecting to web URL in Power BI Desktop? Usually, when we set refresh for dataset in Power BI Service, we choose the same authentication method as Power BI Desktop’s when editing credential in the above screenshot.