Please NOTE that you do not need firebase to get the necessary files and SHA1 hashes - see the guide below if you don't want to use firebase.
If you don't already have a project in Firebase you need to create one in order to generate credentials for an iOS and Android application.
- Add your iOS and Android App inside Project settings (see image).
- Enter required information and download the config file.
Note: For Android, adding the SHA1 hash is an obligation
You can use your debug keystore's SHA1 hash, read this StackOverflow thread to obtain it. When running the keytool command, MAKE SURE you provide path to the correct keystore, you may have multiple keystores on your system! (eg in home directory, and also directly in the android/app folder). To see what keystore is being used to sign your app, go to android/app/build.gradle and look for storeFile entries.
If you don't have a keystore, you need to generate one. To generate your keystore follow this guide.
IMPORTANT if you have multiple keystores (and you likely do - eg. debug and release) you'll need to get the SHA1 hashes for all of them and save the hashes to Firebase!
Follow these instructions from the official docs:
Follow the instructions to Configure a Google API Project from the official docs.
webClientId will be automatically generated once you create the app in the firebase console or configure the API. You can access it here.
Make sure you select the correct project. webClientId should be under OAuth section.