Solution Environment:
Portal for ArcGIS 10.6.1 (Fresh Build)
ArcGIS Server 10.6.1 Standard Edition
Context and Problem statement:
I am using COTS edit widget in WAB enterprise portal application. There are requirements to edit related records from feature layers with one to many relationship.

Goal: I want to auto populate value of primary/key fields F1 & F2 of parent feature layers into fields of destination feature layers while editing feature using Edit Widget in WAB Portal.