Do not have white labeled redirect URL .
We are a retail application company. Our application "iVend Retail" is a desktop application which is installed on-premise. We would like to connect Magento to integrate via REST APIs with oAuth authentication where it seems we need to provide a white labelled Redirect URL. However, our application is installed at many customer sites, therefore we cannot have single Redirect URL. Kindly reply back at earliest to explain how we can overcome this situation.
so exactly you would like to pass data from your desktop app to magento ? or magento store to desktop app ?
If its one directional like magento 2 to your desktop application - then magento 2 have Various types of REST API available.
so you can directly use those api into your application.
here is the magento2 api link - https://devdocs.magento.com/swagger/
We know magento provides various API.
How to handle the authentication in both directions Magento to Desktop Application and from the desktop application to Magento?
okay - i understand !!
Well from your desktop if you would like to do authentication magento 2 have Token based authentication and oAuth based authentication as well.
so you can use any one of them based on your desktop application adapts that and able to get the result.
same way if you would like to access your desktop application api into magento2 then it required specific url with access token or oauth authentication for the same.
so magento 2 system will call that url and do authentication first and then respectively calls other apis for the same.
Hope it helps !!