retrieve template data dynamically

retrieve template data dynamically

A custom templates is created from the ServiceDesk portal. Now I'm trying to add requests to the servicedesk plus using REST API .
At first , in my portal page , i present to the requester  the names of all servicedesk plus services templates ( PC maintenance , slow in internet ,..... etc ) ,  I want when the requester select service template , my system retrieve the field's names to the selected template dynamically ( default fields  subject , description , priority ,  status ,.....  and custom fields  port_number , direct_manager_id , building_no , mobile_no ,.....etc)  , the requester fill the template form my portal and add request to the servicedesk plus. 

please how to achieve this ? 

thank you very much 

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