SWOOP for SharePoint scans page content for hyperlinks (URLs). It will try to access the link and if the response from the target webpage is invalid then the link is set as 'broken'.
In other words, anything the SWOOP for SharePoint data miner does not have access to is considered 'broken'. Technically, we look for the target webpage (i.e. if it returns an error code 4xx or 5xx).
If the page returns a 200 code (e.g. when asking for login), then it is not recorded as a broken link. The same applies if the page redirects to a login page.