Access/use details of Facebook user account such as username,password with my application

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PHP

Facebook-API

Hi All,

I have my website(application) in Andriod and its webservice is in PHP. We have created a login form for this and a registration form for new user. When user register using my application its data is saved to my database in mysql.

Now,the main problem is here, If user logs in with Facebook then this user should be able to access my application. but as my website has no details of this user it will always give error as not a valid user as I have created a HMAC hash value using timestamp,userId and the user password while login.If user data is available in my database then it gives details of user of my application(website).

Is there any way,please suggest