You can sign existing users in and sign new users up with Firebase, as well as tracking events in your app for analytics purposes. First import the Google Play Services file for your Firebase app into your Dropsource app Settings, then use the Firebase authentication and event Actions:
See Authenticate the User with Firebase for more details.
To log your user into Facebook, add the Log User in with Facebook Action to an Event, such as a page loading. You will need to specify the details for an app created via a Facebook Developer account.
The setup is slightly different between iOS and Android:
Use the Invite Facebook Friends Action in conjunction with the login Action to allow users to invite their friends to join your app or service. You can also use Facebook App Event logging in your app by adding the Activate Facebook App Events Action to the Application Launched Lifecycle Event.
You can see GitHub login in action by creating a new project and choosing the GitHub IT Example App. With the project open, select the Login page, click the Login Button Element, and open its Tapped Event.
The Action requires the details of an app that you’ve created via a GitHub Developer account, including a client ID, secret, and callback URL. You can request different levels of scope for the access your app needs to have. See Log the User into GitHub for the full process.