How to approach auto login across multiple ios apps?

Question

I am implementing the feature of automatically logging in the user in an iOS app. This is easy for a single app as we can persist the username with NSUserDefaults while the password using System Keychain.

Now, I want to do it across multiple apps. In my understanding, we'd need a unique device identifier for this, which we can pass to the server and then use it to activate auto login across multiple apps on the same device. Now since, Apple prohibits the use of UDID now, I am thinking of using the Vendor Identifier which would of course require me to set the Bundle IDs accordingly. Is this the best way possible? Or is there a better standard method that is more effective?

Also, Is it at all possible to have auto login between different devices? Like for e.g. If I login on one iOS device and then open the app in another, I should automatically sign in.

Answer 1

To implement login between multiple iOS apps you can use the same App ID prefix in them. It will work because they will share keychain data. Here you can find more details: https://developer.apple.com/library/ios/technotes/tn2311/_index.html

And here the related question: Keychain group access to share data between my existing applications

And about automatic sign in between different devices. I used encrypted iCloud Key Value storage to store login & password between devices. And it worked but not too good. Problem is that first time you start app on new device it will take some time to sync data from iCloud to local storage. And this means that first time you trying to Sign In and may need to wait for some undefined time. In may case it was about 20 seconds. To long for Sign In in a good application :) And of course this require user to be logged in iCloud with the same Apple ID.

ASAIK there is no proper way to implement automatic Sign In from multiple devices. And Apple recommend just to ask for Sign In on every new device of user.