Implement Facebook Login/signup functionality by creating facebook sdk app.

Followings are the steps to create facebook login/signup functionality on server end : 

1) Login with facebook developers .

2) Create an app , Put your domain link where you want to execute the facebook login and fill other options like email id, app name , app image etc.

3) Make created app live by clicking "live" button  and copy down the app id to use it in our server.

Following is the sample html snippet on clicking the facebook login pop up will be generated.

<button type="button" class="connect-fb" onclick="fbLogin();" id="fb-login">Login With Facebook</button>

Put the following script in your html file for facebook login

<script type="text/javascript">

window.fbAsyncInit = function() {
    FB.init({
        appId: '/* paste ur app id here .for eg. 542345324532 */', 
        status: true,
        cookie: true,
        xfbml: true,
        oauth: true
    });
}

function fbLogin() {
    
    FB.login(function(response) {

        if (response.authResponse) {
            FB.api('/me?fields=email,name', function(response) {
                console.log(response);
                 var access_token =   FB.getAuthResponse()['accessToken'];
                    /*  You can use response variable for further use like storing in db for signup or login authentication etc. */
            });
        } else {
            console.log('User cancelled login or did not fully authorize.');
        }
    },
    {
        scope: 'public_profile,email'
    });
}
(function(d) {
    var js,
    id = 'facebook-jssdk';
    if (d.getElementById(id)) {
        return;
    }
    js = d.createElement('script');
    js.id = id;
    js.async = true;
    js.src = "//connect.facebook.net/en_US/all.js";
    d.getElementsByTagName('head')[0].appendChild(js);
} (document));
</script>