.net core lock language

@charettedavid Here is the solution

OnRedirectToIdentityProvider = context =>
{
// More dynamic approach would be using request context
var requestCulture = context.Request.HttpContext.Features.Get<IRequestCultureFeature>();
                        var code = requestCulture.RequestCulture.UICulture.TwoLetterISOLanguageName;
                        context.ProtocolMessage.SetParameter("lang", code);
// Here you can set additional parameters that will be appended to the query string and hence available in lock
return Task.CompletedTask;
}

You might need to parse the query strings in script section of login page the extract values if they are not default Auth0 config settings