Is it possible to configure the web Lock hosted page to just show login for Social Connection and don’t show the username and password fields?
Yes, by default the Lock instance used in the hosted login page (HLP) will only show the connections enabled for the client application that initiated the request so if you have a client application that only wants to support social connections then you should not enable any database (username/password) connection in the client settings.
If you are in the situation that the client application needs to support a database connection, but you just don’t want to show it in the HLP then you can can customize it and set the allowedConnections options. For example:
allowedConnections: 'twitter', 'facebook', 'linkedin']
The above would result in Lock only showing the listed connections even if there were more connections enabled for the client application.