Expose MapUserFn for NewCustomServer

[cdanyl]

Using NewCustomServer how can use MapUserFn?

auth/v2/provider/custom_server.go

Line 49 in 4e32f30

MapUserFn: defaultMapUserFn,

to be able to do something like

auth/v2/provider/providers.go

Line 33 in 78537e6

ID: "google_" + token.HashID(sha1.New(), data.Value("sub")),

My problem using a customServer, i am blocked with an error provider is not allowed.

A custom provider with name provider doesn't create a user.id equal to provider_1234567890

auth/middleware/auth.go

Line 159 in cea049c

func (a *Authenticator) isProviderAllowed(userID string) bool {

func newOauth2Provider(
	goauth2 *goauth2.Server,
	oauth2Config *config.Oauth2,
	oauth2loginPageHandler http.HandlerFunc,
	oauth2Logger *OAuth2Logger,
) *provider.CustomServer {
	serverOption := provider.CustomServerOpt{
		URL:              oauth2Config.Server,
		L:                oauth2Logger,
		LoginPageHandler: oauth2loginPageHandler,
	}

	prov := provider.NewCustomServer(goauth2, serverOption)

	return prov
}

server.AddCustomProvider("provider", client, oauth2Provider.HandlerOpt)

Maybe i am doing something wrong, but i think is good idea to expose MapUserFn

Maybe related : umputun/remark42#1660 (comment)