The Sign In action will pull up the sign in screen for the user.
For the Sign in action to work, your app's privacy settings must be set to Public, with either optional or required sign-in, where Anyone can create a profile. The sign-in action will only appear if the user is not signed in yet.
Click on the plus (+) sign in the Components panel and select the Component you want to trigger the action.
In the General tab on the right side of the Layout Editor, navigate to the Actions section and select Sign in.
Select the icon and descriptive text to use in your app. Success shares the descriptive text on a green background, and Failure shares the descriptive text on a red background.
You can optionally add Conditions for certain criteria to be met before a user can trigger this action.
Select the + New Action button. If you have existing actions, click on the plus (+) sign in the left panel.
Select the data source for your action.
Configure your first action by clicking the first action in the sequence. You can also add Conditions to your actions, if needed.
To add new actions to the flow, hover just underneath an action and click the plus button. In this way you can add the Sign In action as just one step in a larger workflow.
Check the Introduction to Actions page for a full list of components that can be used to trigger actions.