Hi @sagarjoshi,
Answer to your question regarding authentication in Power Apps Portal WebApi for CRUD operations, they have a wrapper ajax function that takes care of the token from the current logged in user's session. Also you can control the field in entities to expose it WebApi CRUD operations.
Ex:
(function(webapi, $){ function safeAjax(ajaxOptions) { var deferredAjax = $.Deferred(); shell.getTokenDeferred().done(function (token) { if (!ajaxOptions.headers) {
To get the complete code for CRUD operations in Power Apps Portal, please use the below link:
https://docs.microsoft.com/en-us/powerapps/maker/portals/web-api-perform-operations#web-api-ajax-samples
--------------------------------------------------------------------------
If you feel my reply is satisfactory, please accept it as solution. Thanks!!