How can i access facebook without entering access token in unity project???

Actually i have made my unity project and have linked it with facebook after making an app on developers.facebook.com.Now i want that when i click on login to facebook button then it prompt me to enter my user id and password at 1st time...How is it possible???Then after that when i click on the login button.it automatically link to my facebook id.please help me to solve this issue...its urgent...