Setting Custom Field Values in Customer Requests on the Jira Service Management Portal

I have developed a custom field type using Forge for Jira Software. Now, I’m working on an extension to support Jira Service Management with the modules jiraServiceManagement:portalRequestCreatePropertyPanel and jiraServiceManagement:portalRequestDetail. Everything is functioning as expected.

However, I have a question: when a customer creates a request on the portal, what is the best method to set the value of the custom field type for the issue?