How to add Facebook Login in Android

// Facebook login
  compile 'com.facebook.android:facebook-android-sdk:4.21.1'

/**
 * Created by Andy
 * An utility for Facebook
 */
public class FacebookSignInHelper {
    private static final String TAG = FacebookSignInHelper.class.getSimpleName();
    private static FacebookSignInHelper facebookSignInHelper = null;
    private CallbackManager callbackManager;
    private Activity mActivity;
    private static final Collection<String> PERMISSION_LOGIN = (Collection<String>) Arrays.asList("public_profile", "user_friends","email");
    private FacebookCallback<LoginResult> loginCallback;

    public static FacebookSignInHelper newInstance(Activity context) {
        if (facebookSignInHelper == null)
            facebookSignInHelper = new FacebookSignInHelper(context);
        return facebookSignInHelper;
    }

    public FacebookSignInHelper(Activity mActivity) {
        try {
            this.mActivity = mActivity;
            // Initialize the SDK before executing any other operations,
            // especially, if you're using Facebook UI elements.
            FacebookSdk.sdkInitialize(this.mActivity);
            callbackManager = CallbackManager.Factory.create();
            loginCallback = new FacebookCallback<LoginResult>() {
                @Override
                public void onSuccess(LoginResult loginResult) {
                   // You are logged into Facebook
                }

                @Override
                public void onCancel() {
                    Log.d(TAG, "Facebook: Cancelled by user");
                }

                @Override
                public void onError(FacebookException error) {
                    Log.d(TAG, "FacebookException: " + error.getMessage());
                }
            };
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * To login user on facebook without default Facebook button
     */
    public void loginUser() {
        try {
            LoginManager.getInstance().registerCallback(callbackManager, loginCallback);
            LoginManager.getInstance().logInWithReadPermissions(this.mActivity, PERMISSION_LOGIN);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    

    /**
     * To log out user from facebook
     */
    public void signOut() {
        // Facebook sign out
        LoginManager.getInstance().logOut();
    }

    public CallbackManager getCallbackManager() {
        return callbackManager;
    }

    public FacebookCallback<LoginResult> getLoginCallback() {
        return loginCallback;
    }

    /**
     * Attempts to log debug key hash for facebook
     *
     * @param context : A reference to context
     * @return : A facebook debug key hash
     */
    public static String getKeyHash(Context context) {
        String keyHash = null;
        try {
            PackageInfo info = context.getPackageManager().getPackageInfo(
                    context.getPackageName(),
                    PackageManager.GET_SIGNATURES);
            for (Signature signature : info.signatures) {
                MessageDigest md = MessageDigest.getInstance("SHA");
                md.update(signature.toByteArray());
                keyHash = Base64.encodeToString(md.digest(), Base64.DEFAULT);
                Log.d(TAG, "KeyHash:" + keyHash);
            }
        } catch (PackageManager.NameNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return keyHash;
    }
}

FacebookSignInHelper facebookSignInHelper = FacebookSignInHelper.newInstance(LoginActivity.this, fireBaseAuthHelper);
facebookSignInHelper.loginUser();

facebookSignInHelper.getCallbackManager().onActivityResult(requestCode, resultCode, data);