Need read-only custom fields that will fetch data via REST API

[Amine Filali]

In the create screen, I have a custom field that will be filled by the user and I need several readonly custom fields that have to fetch data via REST API depending on what the user has filled. 

For example:

• Let's say I have one editable custom field : "social security number" and 2 readonly fields : First Name & Last Name
• Requirement : As a user I want to fill the social security number in the create issue screen and the other two readonly fields have to display the First Name and the Last Name of the person holding the social security number after calling a REST API and giving it as an argument the social security number that the user typed. 

How can I achieve this? 

thank you in advance