I am currently using Firebase passwordless email verification for authentication to deep link from the email verification link to my iOS app. I would like the verification link to have the form https://example.com/onboard/<otherparams>. This would allow me to specify in the apple-app-site-association file that links that contain /onboard/* should link to my app while others should not.
Unfortunately, even when I use https://example.com/onboard in the "Action URL" field of the email template on the Firebase console, the verification link emailed to the user is in the form https://example.com/?link=https://example.com/onboard?apiKey.... I'm able to get the authentication working when I specify in the apple-app-site-association file that links that contain /* should open the app. However, this is an issue because I don't want other links to my domain (such as https://example.com/terms) to open my app.
What is causing Firebase to not create the verification link in the form https://example.com/onboard/<otherparams>?