App-LinkedIn Connection

We have a cross-platform mobile app (built on Cordova/Ionic). The app requires users to sign up via LinkedIn in order to use it, because it is for professional networking. In the sign-up process, the users is directed to an empty LinkedIn login page to enter their username and password, even though they have the LinkedIn app on their phone and already authorized. This has turned away many users from our app as they do not trust the sign-up process. We are trying to use direct LinkedIn sign-up, i.e. if the user has the LinkedIn app and starts using our app it should just show them a page saying "Allow" and not ask for their username/password again -- but our developers told us this is currently not possible with cross-platform apps and can only be done with native coding. We are not convinced with this and are offering this project for a developer who can find a solution for this problem, and get the single sign-up feature to work on our app.