Looking for information or example of Invoke API

Looking for information or example of Invoke API

I am looking to invoke: https://desk.zoho.com/DeskAPIDocument#Tickets#Tickets_Getaticket from my extension. I am currently opening up a HTTPRequest for it and filling the fields as needed. I believe I have it correct but am running into CORS issues: Access to XMLHttpRequest at 'https://desk.zoho.com/api/v1/invoke?{orgId}' from origin 'https://127.0.0.1:5000' has been blocked by CORS policy: No 'Access-Control-Allow-Origin'. Is it possible to get a solid example of invoking this API for reference? 

Side issue: I am confused on how to get my securityContext. Help with this would be appreciated also.
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