I'm trying to integrate an app-in billing into a flex mobile application. I found this page : http://www.adobe.com/devnet/flex/articles/flex_paypal.html
It seems to work but, for security purposes (store Paypal credentials), I had to install a web app on my web server.
I had a look on the libraries (MPL) for android and ios SDKs, they don't seem to call a web server.
Does someone know if there's a way to avoid installing this server?
The linked article is an excellent treatment of integrating PayPal's Adaptive Payments product from the perspective of a Flex/AIR single-page web app. However, this product (Adaptive Payments) would not be recommended for use in a mobile app rather than a browser due to the different security features of apps (with embedded minibrowsers) vs. browser environments.
The MPL libraries have also been deprecated in favor of PayPal's newest mobile SDKs. See:
https://developer.paypal.com/docs/integration/mobile/mobile-sdk-overview/
I would recommend looking into using either these newest PayPal SDKs, or mobile Braintree SDKs that combine PayPal and Braintree card acceptance in a single SDK, as the most secure & having the best mobile user experiences (and the most likely to be supported well into the future).
These SDKs do not require you to have a web server that hosts any pages for user interaction (e.g. a page that redirects a user to PayPal, or one that handles a redirection back). They provide libraries for the secure collection & validation of the user's credentials from inside your app.
That said, you still need to maintain the security of your PayPal API credentials access. The latest SDKs (as referenced above) allow you to generate access tokens for a particular device while keeping your account credentials secure on your server. But you do need that server, and your mobile app will need to communicate with it to become authenticated to make calls to PayPal on your behalf; otherwise your full PayPal API credentials would have to be sent to every device on which your app is installed, which would not be wise.
