When an OAuth2 client requests a new Authorization, the server shows a web page where the user must allow the connection and then login. This page is provided by sgcWebSockets library and is dispatched automatically when a client requests an Authorization.

If the user Allows the access, a login form will be shown where the user must set the Username and Password.
This data will be received OnOAuth2Authentication event, so you must validate than the user/password is correct and if it is, then set Authenticated parameter to true.
void OnOAuth2Authentication(TsgcWSConnection Connection, TsgcHTTPOAuth2Request OAuth2, string aUser,
string aPassword, ref bool Authenticated)
{
if ((aUser == "user") and (aPassword == "secret"))
{
Authenticated = true;
}
}