google plus integration issue in swift 3.0

Question

func finishedWithAuth(auth: GTMOAuth2Authentication!, error: NSError!) {
    let plusService :GTLServicePlus = GTLServicePlus.init()
    plusService.retryEnabled = true
    plusService.authorizer = GPPSignIn.sharedInstance().authentication
    plusService.apiVersion = "v1"

    let query : GTLQueryPlus = GTLQueryPlus.queryForPeopleGetWithUserId("me") as! GTLQueryPlus

    plusService.executeQuery(query) { (ticket,person, error) -> Void in
        if ((error) != nil) {
            //Handle Error
        } else {
           // NSLog("Email= %@", GPPSignIn.sharedInstance().authentication.userEmail)
           // NSLog("GoogleID=%@", person.identifier)
            print(person)
            print(person.aboutMe)
        }
    }

}

when we build always getting authentication fail in swift 3.0 in GTMOAuth2Authentication , so can you please help me