The HTTP service's authentication setting (username and password) doesn't work with Schneider Electric HMI's that are using Web Viewer to visualize the HMI pages on a web server.
Schneider Electric's Web Viewer doesn't support any HTTP(S) authentication method (source: Schneider Electric Support).
None. However, you may contact Schneider Electric to request that this be supported in a future version of the Web Viewer.
Note that the HTTP service can still be used to easily connect to the HMI, but authentication (username and password) will need to be entered manually every time you connect.