유저 검증 (User Verify)

if(GIDSignIn.sharedInstance.hasPreviousSignIn()) {
    GIDSignIn.sharedInstance.restorePreviousSignIn()
    // 로그인 이후 액션
} else {
    // 로그인 뷰로 이동
}

프로필 정보 가져오기 (User Profile)

GIDSignIn.sharedInstance.signIn(with: signInConfig, presenting: self) { user, error in
    guard error == nil else { return }
    guard let user = user else { return }

    let emailAddress = user.profile?.email

    let fullName = user.profile?.name
    let givenName = user.profile?.givenName
    let familyName = user.profile?.familyName

    let profilePicUrl = user.profile?.imageURL(withDimension: 320)
}

로그아웃 (Sign Out)

GIDSignIn.sharedInstance.signout()

let firebaseAuth = Auth.auth()
do {
  try firebaseAuth.signOut()
} catch let signOutError as NSError {
  print("Error signing out: %@", signOutError)
}

연결 해제 (Disconnect)

GIDSignIn.sharedInstance.disconnect { error in
    guard error == nil else { return }

    // Google Account disconnected from your app.
    // Perform clean-up actions, such as deleting data associated with the
    //   disconnected account.
}