Creating an Odata webService for an external app

Hi everyone,

First of all, sorry for all the text, but I found myself into a new and big development for me.

I must publish as a REST webService different fields from a ítem.

To publish as REST, I must use oData, so query or page are the options. I decided to use page for one simple reason. There is a value to send, “availabilty”, that is the difference between the inventory and quantity on sales order. That value is not a field into the ítem table, is returned by a function, so I must use a variable to take that value. The only way to show that variable is using a page, the query doesn’t allow it, so that’s the reason.

Ibn this way, the app recevices perfectly the al the data from the ítems, but we must go one step more. The app calls the api with an URL like this:

Here we can se 2 important issues:

-Server paging: The webService msut receive as parameters the page number an the page size. For example, if page is 3, and page size 20, we must send items 41 to 60.

-Authentication: The webService also receives a sign, that must be decrypted and if it's correct, we will send the data to the external app.

I'm in touch with the developer of the app, but I don't know what will be the best approach to this development. We've also thought about programing a web API in visual studio... The paging, and mostly, the authentication part, seems that requires a web API, but I'm not sure, I've never worked with one...

I will appreciate any hint about how route this development, before starting to think about the technical part, because I'm quite lost with this.. it's a development for NAV 2018 by the way

Thank you all again