Forgotten Password code for OpenIdConnect

Questions
1

We have used this example https://github.com/jbreuer/Umbraco-OpenIdConnect-Example to set up B2C for a client. However now need to do the Forgotten Password functionality. I have added this in:

options.Events.OnRemoteFailure = context =>
{
    var message = context.Failure?.Message;
    if (message != null && message.Contains("AADB2C90118"))
    {
        // Password reset requested
        var passwordResetPolicy = config["OpenIdConnect:PasswordResetPolicyId"];
        var redirectUrl = "/umbraco/externallogin/OpenIdConnect?policy=" + passwordResetPolicy;

        context.Response.Redirect(redirectUrl);
        context.HandleResponse();
    }
    return Task.CompletedTask;
};

With various different combinations and permutations of the redirectUrl part, both with and without umbraco/externallogin etc. Nothing works, it all comes back with 404. Has anyone successfully implemented this? Thanks