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Some providers like Facebook and Dropbox support authentication by launching into their iOS app directly rather than using Safari or other web views.

Add specifics schemes

iOS 9 requires your app to pre-register application schemes it intends to call. For each provider, you’ll need to add specifics schemes to your list of allowed schemes

• For Dropbox: dbapi-2, db-<APP_KEY>
• For Facebook: fbauth2, fb<APP_KEY>

Open your YourApp-Info.plist file and add the key, LSApplicationQueriesSchemes.

Under LSApplicationQueriesSchemes, add a new item with the value dbapi-2(resp. fbauth2) It should look like this in the source code for your Info.plist file:

<key>LSApplicationQueriesSchemes</key>
<array>
  <string>dbapi-2</string>
</array>

This will allow to call the native app as part of the authentication flow.

Choose authorizeURLHandler

Use OAuthSwiftOpenURLExternally instance to open authorize url in the native app

oauthswift.authorizeURLHandler = OAuthSwiftOpenURLExternally.sharedInstance

Check native app installed

Then before authentificate you can test is the native app is installed by doing for instance for dropbox on iOS

var isDropboxAppInstalled: Bool = {
    let appUrl = URL(string: "dbapi-2://app")
    return UIApplication.shared.canOpenURL(appUrl!)
}()

Define an authorize Url

Then you can use an authorizeUrl like this :

• for dropbox: "dbapi-2://1/connect?k=(dropboxAppId)&s=&state=oauth2:(nonce)" where nonce is random state string. Dropbox example uses UUID().uuidString.
• for facebook "fbauth2://authorize?response_type=token&client_id=(facebookAppId)&redirect_uri=fb(facebookAppId)&scope=public_profile" with OAuth2Swift

Handle callback url

The native app will call back into your app using the fb<APP_KEY> or db<APP_KEY>- url scheme defined before and used as callbackURL with the appropriate token:

func application(_ app: UIApplication, open url: URL, options: [UIApplicationOpenURLOptionsKey : Any] = [:]) -> Bool {
    if (url.host == "oauth-callback") || (url.scheme == "fb<APP_KEY>) { // probably check source too
        OAuthSwift.handle(url: url)
    }
    return true
}

⚠️ For dropbox the callback does not match what OAuthSwift/OAuth expectations though - it is almost more closely appears like an OAuth v1 response with oauth_token_secret being the important value: db-<APP_KEY>://1/connect?oauth_token_secret=<MY_SECRET>&state=oauth2%3A&uid=<DROPBOX_USER_ID>&oauth_token=oauth2%3A (Note that the %3A is just : url encoded.)

So you would need to either rewrite the url query before passing it into OAuthSwift.handle(url: url), ie. change oauth_token_secret by code

Special Thanks

@mikegray for #300 and words