Create an "App ID" by adding a new "Identifier" here, choose app IDs, enable "Sign in with Apple" enabled.
Create a "Services ID" by adding a new "Identifier" here, choose service IDs, enable "Sign in with Apple".
Click "Configure" the Next to "Sign in with Apple". In "Primary App ID" field, select app ID created above.
Fill in and verify the domain created above, add https://<YOUR_AUTHGEAR_ENDPOINT>/sso/oauth2/callback/apple to Return URLs
Create a "Key" following this guide with "Sign in with Apple" enabled. Click "Configure" next to "Sign in with Apple" and select "Primary App ID" with app ID created above. Keep the private key safe, you need to provide this later.
Redirect URI has the form of /sso/oauth2/callback/:alias. The alias is used as the identifier of OAuth provider. You can configure the alias in Authgear Portal.
Configure Sign in with Apple in Authgear Portal
In the portal, go to Single-Sign On page in your project
Enable Sign in with Apple
Fill in the Client ID with the Service ID obtained above.
In Apple Developer Portal, view key information of the "Key" created above
Jot down the Key ID and download the key text file (.p8 file)
Copy the content in the key text file to Client Secret text area in Authgear Portal.
Fill in Key ID field using the Key ID obtained from step 5
In Apple Developer Portal, click username on the top right corner, click View Membership
Find the Team ID from Membership Information, fill in Team ID field in Authgear portal
Save the settings
🎉Done! You have just added Sign in with Apple to your apps!