docs: create migration guide for v9.0

Author: thatfiredev

README.md

@@ -71,6 +71,7 @@ After the project is synchronized, we're ready to start using Firebase functiona
 If you are using an old version of FirebaseUI and upgrading, please see the appropriate
 migration guide:
 
+* [Upgrade from 8.0.2 to 9.x.x](./docs/upgrade-to-9.0.md)
 * [Upgrade from 7.2.0 to 8.x.x](./docs/upgrade-to-8.0.md)
 * [Upgrade from 6.4.0 to 7.x.x](./docs/upgrade-to-7.0.md)
 * [Upgrade from 5.1.0 to 6.x.x](./docs/upgrade-to-6.0.md)

docs/upgrade-to-9.0.md

@@ -0,0 +1,35 @@
+# Upgrading to FirebaseUI 9.0
+
+FirebaseUI version `9.0.0` has significant breaking API changes and also adopts new major versions
+of many critical dependencies. Below is a description of each breaking change.
+
+## All - Update to Firebase BoM 33
+
+FirebaseUI now depends on the Firebase SDK at BoM major version `33.9.0`. You should update your
+app to use the same major version to avoid possible compilation errors or crashes.
+
+For more information on this SDK release see the
+[Firebase Android SDK release notes](https://firebase.google.com/support/release-notes/android#bom_v33-9-0).
+
+Release Notes for other BoM versions with breaking changes:
+- [Firebase Android SDK BoM 32.0.0](https://firebase.google.com/support/release-notes/android#bom_v32-0-0)
+- [Firebase Android SDK BoM 31.0.0](https://firebase.google.com/support/release-notes/android#bom_v31-0-0)
+- [Firebase Android SDK BoM 30.0.0](https://firebase.google.com/support/release-notes/android#bom_v30-0-0)
+- [Firebase Android SDK BoM 29.0.0](https://firebase.google.com/support/release-notes/android#bom_v29-0-0)
+
+## Auth - Remove Smart Lock
+
+TODO
+
+## Auth - (behavior change) new Email authentication flow
+
+Versions 8.x and older of FirebaseUI relied on methods like `fetchSignInForEmail`, which
+now fail with the introduction of
+[Email Enumeration Protection](https://cloud.google.com/identity-platform/docs/admin/email-enumeration-protection).
+
+Version 9.0 removed those methods and now shows a different flow for email sign in and sign up.
+
+## Auth - Removed SafetyNet
+
+[Firebase Auth v22.0.0](https://firebase.google.com/support/release-notes/android#auth_v22-0-0)
+removed SafetyNet support for app verification during phone number authentication.