If you want to build your own custom registration page--which is an excellent idea, because we don't recommend making Identity Internet facing--the best way to do that is to process the registration page in your application, and then [make a back channel call to the Gluu Server SCIM endpoint (i.e. POST to the /Users endpoint)](https://gluu.org/docs/gluu-server/4.1/user-management/scim2/). Note: to call the SCIM /Users endpoint, you need to present an UMA RPT token. When you install community edition, a client is automatically created for you, and you can use that client for your code.
Another way to handle registration is using a person authn interception script. There is a [sample registration authn script here](https://github.com/GluuFederation/oxAuth/tree/master/Server/integrations/custom_registration)