Facebook Login with iOS SDK 4.0 in Swift

FacebookLogin.swift

//If you have a Bridging-Header:
#import <FBSDKCoreKit/FBSDKCoreKit.h>
#import <FBSDKLoginKit/FBSDKLoginKit.h>

//In your AppDelegate:

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [String: AnyObject]?) -> Bool {
    //App launch code
    FBSDKApplicationDelegate.sharedInstance().application(application, didFinishLaunchingWithOptions: launchOptions)
    //Optionally add to ensure your credentials are valid:
    FBSDKLoginManager.renewSystemCredentials { (result:ACAccountCredentialRenewResult, error:NSError!) -> Void in
        //
    }
}

func application(application: UIApplication, openURL url: NSURL, sourceApplication: String?, annotation: AnyObject?) -> Bool {
    //Even though the Facebook SDK can make this determinitaion on its own,
    //let's make sure that the facebook SDK only sees urls intended for it,
    //facebook has enough info already!
    let isFacebookURL = url.scheme != nil && url.scheme!.hasPrefix("fb\(FBSDKSettings.appID())") && url.host == "authorize"
    if isFacebookURL {
        return FBSDKApplicationDelegate.sharedInstance().application(application, openURL: url, sourceApplication: sourceApplication, annotation: annotation)
    }
    return false
}

func applicationDidBecomeActive(application: UIApplication) {
    //App activation code
    FBSDKAppEvents.activateApp()
}

//Here's the facebook login code, have your login procedure call this:

let facebookReadPermissions = ["public_profile", "email", "user_friends"]
//Some other options: "user_about_me", "user_birthday", "user_hometown", "user_likes", "user_interests", "user_photos", "friends_photos", "friends_hometown", "friends_location", "friends_education_history"

func loginToFacebookWithSuccess(successBlock: () -> (), andFailure failureBlock: (NSError?) -> ()) {
    
    if FBSDKAccessToken.currentAccessToken() != nil {
        //For debugging, when we want to ensure that facebook login always happens
        //FBSDKLoginManager().logOut()
        //Otherwise do:
        return
    }
    
    FBSDKLoginManager().logInWithReadPermissions(self.facebookReadPermissions, handler: { (result:FBSDKLoginManagerLoginResult!, error:NSError!) -> Void in
        if error != nil {
            //According to Facebook:
            //Errors will rarely occur in the typical login flow because the login dialog
            //presented by Facebook via single sign on will guide the users to resolve any errors.
            
            // Process error
            FBSDKLoginManager().logOut()
            failureBlock(error)
        } else if result.isCancelled {
            // Handle cancellations
            FBSDKLoginManager().logOut()
            failureBlock(nil)
        } else {
            // If you ask for multiple permissions at once, you
            // should check if specific permissions missing
            var allPermsGranted = true
            
            //result.grantedPermissions returns an array of _NSCFString pointers
            let grantedPermissions = result.grantedPermissions.allObjects.map( {"\($0)"} )
            for permission in self.facebookReadPermissions {
                if !contains(grantedPermissions, permission) {
                    allPermsGranted = false
                    break
                }
            }
            if allPermsGranted {
                // Do work
                let fbToken = result.token.tokenString
                let fbUserID = resutl.token.userID
                
                //Send fbToken and fbUserID to your web API for processing, or just hang on to that locally if needed
                //self.post("myserver/myendpoint", parameters: ["token": fbToken, "userID": fbUserId]) {(error: NSError?) ->() in
                //	if error != nil {
                //		failureBlock(error)
                //	} else {
                //		successBlock(maybeSomeInfoHere?)
                //	}
                //}
                
                successBlock()
            } else {
                //The user did not grant all permissions requested
                //Discover which permissions are granted
                //and if you can live without the declined ones
                
                failureBlock((nil)
            }
        }
    })
}

thank you for a very valuable post and discussion; took me some time to make it work for Swift 2.2 though, so here is my version. Yes, you might want to make it more pretty with guard statements etc. but I just needed this to work for now...

AppDelegate.swift excerpt

// according to SDK documentation, this is now possible, check https://developers.facebook.com/docs/ios/getting-started/advanced#swift
import FBSDKCoreKit
import FBSDKShareKit
import FBSDKLoginKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?


    func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
        // Override point for customization after application launch.

        //App launch code
        FBSDKApplicationDelegate.sharedInstance().application(application, didFinishLaunchingWithOptions: launchOptions)
        //Optionally add to ensure your credentials are valid:
        FBSDKLoginManager.renewSystemCredentials { (result:ACAccountCredentialRenewResult, error:NSError!) -> Void in
            //
        }

        return true
    }

    func application(application: UIApplication, openURL url: NSURL, sourceApplication: String?, annotation: AnyObject) -> Bool {
        //Even though the Facebook SDK can make this determinitaion on its own,
        //let's make sure that the facebook SDK only sees urls intended for it,
        //facebook has enough info already!
        guard url.scheme.hasPrefix("fb\(FBSDKSettings.appID())") && url.host == "authorize" else {
            return false
        }

        return FBSDKApplicationDelegate.sharedInstance().application(application, openURL: url, sourceApplication: sourceApplication, annotation: annotation)

    }

    func applicationDidBecomeActive(application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.

        //App activation code
        FBSDKAppEvents.activateApp()
    }
// . . .
}

FacebookLoginClient.swift

import Foundation

// according to SDK documentation, this is now possible, check https://developers.facebook.com/docs/ios/getting-started/advanced#swift
import FBSDKCoreKit
import FBSDKShareKit
import FBSDKLoginKit


let facebookReadPermissions = ["public_profile", "email", "user_friends"]
//Some other options: "user_about_me", "user_birthday", "user_hometown", "user_likes", "user_interests", "user_photos", "friends_photos", "friends_hometown", "friends_location", "friends_education_history"

func loginToFacebookWithSuccess(callingViewController: UIViewController, successBlock: () -> (), andFailure failureBlock: (NSError?) -> ()) {

    if FBSDKAccessToken.currentAccessToken() != nil {
        //For debugging, when we want to ensure that facebook login always happens
        //FBSDKLoginManager().logOut()
        //Otherwise do:
        return
    }

    FBSDKLoginManager().logInWithReadPermissions(facebookReadPermissions, fromViewController: callingViewController, handler: { (result:FBSDKLoginManagerLoginResult!, error:NSError!) -> Void in
        if error != nil {
            //According to Facebook:
            //Errors will rarely occur in the typical login flow because the login dialog
            //presented by Facebook via single sign on will guide the users to resolve any errors.

            // Process error
            FBSDKLoginManager().logOut()
            failureBlock(error)
        } else if result.isCancelled {
            // Handle cancellations
            FBSDKLoginManager().logOut()
            failureBlock(nil)
        } else {
            // If you ask for multiple permissions at once, you
            // should check if specific permissions missing
            var allPermsGranted = true

            //result.grantedPermissions returns an array of _NSCFString pointers
            let grantedPermissions = Array(result.grantedPermissions).map( {"\($0)"} )
            for permission in facebookReadPermissions {
                if !grantedPermissions.contains(permission) {
                    allPermsGranted = false
                    break
                }
            }
            if allPermsGranted {
                // Do work
                let fbToken = result.token.tokenString
                let fbUserID = result.token.userID

                //Send fbToken and fbUserID to your web API for processing, or just hang on to that locally if needed
                //self.post("myserver/myendpoint", parameters: ["token": fbToken, "userID": fbUserId]) {(error: NSError?) ->() in
                //  if error != nil {
                //      failureBlock(error)
                //  } else {
                //      successBlock(maybeSomeInfoHere?)
                //  }
                //}

                successBlock()
            } else {
                //The user did not grant all permissions requested
                //Discover which permissions are granted
                //and if you can live without the declined ones
                failureBlock(nil)
            }
        }
    })
}