• This library user for firebase integration dependencies

{ 
   implementation 'com.google.firebase:firebase-auth:19.4.0'
}

• This permission use internet connection checking

{
<com.facebook.login.widget.LoginButton          
android:id="@+id/login_button"          
android:layout_width="match_parent"          
android:layout_height="match_parent"          
android:layout_gravity="center"
android:visibility="gone"/>
}

• This permission is for user data. Without this permission user data not meet
  
  
• loginButtonThis button is Facebook button
  
  
• LoginManager.getInstance().logInWithReadPermissions(FacebookLoginActivity.this, Arrays.asList("email", "public_profile"));
• loginButton.setReadPermissions("email", "public_profile");

void initializeAuthentication(){
   FirebaseAuth  mAuth = FirebaseAuth.getInstance();
   GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
   .requestIdToken(getString(R.string.default_web_client_id))
   .requestEmail()
   .build();
   mGoogleSignInClient = GoogleSignIn.getClient(this, so); 
}

• This function user login result return

void faceBookLogin(LoginResult loginResult){
   setFacebookData(loginResult);
   Profile profile = Profile.getCurrentProfile();      
   if (profile != null) {        
      String avatar = ImageRequest.getProfilePictureUri(profile.getId(), 200, 200)
     .toString();    
   }    handleFacebookAccessToken(loginResult.getAccessToken());
}

• This token return firebase login fails or not an event

private void handleFacebookAccessToken(AccessToken token) {
AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());
mAuth.signInWithCredential(credential)           
.addOnCompleteListener(this, new OnCompleteListener() {                
      @Override                
      public void onComplete(@NonNull Task task) {
      if (task.isSuccessful()) {
      FirebaseUser user = mAuth.getCurrentUser();
      user.getIdToken(true).addOnCompleteListener(new OnCompleteListener() {
      @Override
      public void onComplete(@NonNull Task task) {
            String token = task.getResult().getToken();
       }
    });
 } else {
      String errorCode = String.valueOf(task.getException());
      Toast.makeText(FacebookLoginActivity.this, "Login failed.", Toast.LENGTH_SHORT).show();
                    } 
            }
    });
}

• “Default_web_client_id” this keyword, not changes because creating google-services.json file time automatically this keyword in add values so this key work put at its