This has been discussed a couple o’ times before already – but I mostly commented on earlier questions, so let me write the whole thing up as a proper answer, for future reference.
[paraphrased] Multiple-client Facebook login via one single app id
Does anyone have a direction for me?
You probably rather don’t want to do that.
It is not really possible to run one simple app one multiple different domains.
As a workaround for only a few domains, people used to specify different domains for the different platforms – Website, Page Tab or Canvas App, plus Mobile alternative for Canvas – without actually using any of those platforms besides Website, which made the app usable on multiple domains as a website app. But since Facebook introduced their login/permission review process1, you can’t do that any more – they expect you to present actual functionality on all platforms you have configured in your app.
You can kind-off use one single app for login on multiple domains – if you are willing to use only the server-side login flow, and to redirect users to one “main” domain (that gets specified as the app domain in the app settings) to login, and then from there back to the origin domain.
But this has several drawbacks:
It’s not what you’d call a “white label” solution. If your clients expect it to look as if users where logging in via “their” app, it should stay on their domain. Individual branding, in regard to stuff such as app name, app logo that shows in the login dialog, etc., would also not be possible. Additionally, app attribution – the link that shows up under content shared/posted via the app – would only link users back to the main domain, and not to your customer’s.
You would not be able to use the JS SDK for client-side API requests, or even just to embed it to render any of the FB social plugins that require an app id – the SDK checks what domain it is “running on”, and can not be tricked to accept a domain that is not specified in the app settings.
There could be privacy issues. An over-exaggerated example: Just because I as the app user decided to share my photos or videos I have on Facebook with your customer Our-Holy-Mother-of-Christ-Bakery.com, does not necessarily mean I want to share them with your other customer, amateurs-doing-all-kinds-of-nasty-stuff.xxx as well – but if they shared an app id for login purposes, I automatically would. Have fun writin’ the Privacy Policy (which is mandatory if you use FB login functionality, and FB also automatically checks if your app has got one) for that scenario ;-)
Finally, and most importantly: All your customers would be “sitting in the same boat.” If one of them, or in turn their website users, would publish spam via your app id, so that Facebook blocks it, login would not work any more for all of your customer’s websites. And if you decide only then, that setting up an individual app for each of your customers would be the better way to go, they would not be able to recognize their existing users any more, because of user ids being app-scoped since API v2.0 was introduced – so if users logged into this new app, that app would see a totally different user id. (And to rely on an email address as an identifier is risky, too, because you will not get one from the API for every user; for example if they registered using their mobile device.)
Edit: Plus, app/domain insights, as luschn mentioned in his answer.
1 Yes, the review process has made it more laborious to set up multiple apps for multiple clients. But for apps that do the same stuff/use the same permissions in the same manner, you can refer to an earlier successfully reviewed app id to speed up the process a little. Also, screenshots of how f.e. posts made via the app look on timeline, and what UI components are used, as well as screencasts that you include in your submission could probably be used with little to no alteration.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
