1. Setup OAuth consent screen

To set up login with google, first you need to setup the Oauth consent Screen for your Firebase application.

Step 1: open the page https://console.developers.google.com

Step 2: In the upper right corner, click the button as shown in the picture (it could be any one of your project names)

Select the project you want to setup. If you cannot find them in the RECENT project list, please click ALL to display them all and select the project.

Step 3: on the left menu, select the OAuth consent screen
Step 4: Choose External and click CREATE

Step 5: Fill in some necessary information on the OAuth consent screen:
- Add Logo and choose support email

- Add Authorized domains or use the default
- Enter  `Application Homepage link`, `Privacy prolicy link`, `Terms of Service link`. If not, use it with the default Authorized domains link (don't forget to add `https://`).
- Click `Save`

Done

2. Setup for IOS

Step 1: Enable Authentication

Open your firebase project, in the left menu bar, select Authentication → Sign-in method → Google

Step 2: Click Enable → choose email support and click Save

Step 2: Create App IOS in project firebase

Back to the project settings page, add the ios application to your project:

In this step, the Bundle ID of the IOS application is required
Open file project.pbxproj in your project flutter at ios/Runner.xcodeproj/project.pbxproj , search with keyword PRODUCT_BUNDLE_IDENTIFIER to get Bundle ID
Return to Firebase page, enter Bundle ID and App nickname (optional).Then click Register app to continue
Before starting the next step, go back to the project flutter, go to the ios folder and delete file GoogleService-info.plist (path: ios/GoogleService-Info.plist)
Download the GoogleService-info.plist file and save it into the ios folder of the project flutter

Click next to continue
Next to continue

Click Skip this step to complete

Step 3: Config file **info.plist** with file GoogleService-info.plist

Next, open the GoogleService-info.plist file, find the key REVERSED_CLIENT_ID, copy the value in the string tag below it.
Open the project's info.plist file, search for the keyword CFBundleURLSchemes (because this file may have many places with this keyword, so you should pay attention to the code in the image below. It is the setup code forCFBundleURLTypes.). Replace the code in the string tag as shown below:
Complete the setup process.

3. Setup for android

Important note:

Because the project is separate between the develop and release, if you are not clear about the problem, you will be mistaken.

When you build the debug, the application will retrieve keystore information at **android/key-debug.properties** . You can get the SHA1 code from the keystore file in folder **android/app**. In the case of using FluxStore's default keystore, the specific keystore path is

android/app/mstore.keystore
When you build release, the keystore information will be stored in folder **android/key.properties**. In the case of a build release, please call the build bundle script for the application to obtain the correct keystore.

Command build release android:

 sh tools / build-appbundle.sh

In this case, the keystore file will be saved in folder certs/ of the project. If you build release, please get the SHA1 code of the keystore file at the path (default of FluxStore)

certs/key.jks

Google sign-in is automatically configured on your connected iOS and web apps. To set up Google sign-in for your Android apps, you need to add the SHA1 fingerprint for each app on your Project Settings.

Step 1: Open Project Settings in your project firebase, add new app android:

Step 2: Enter info your project

- `Android package name` is the android package name in your project flutter. You can find it in file `android/app/src/main/AndroidManifest.xml`

Get SHA certificate fingerprints from file keystore
- Open terminal in your project, call command:
keytool -exportcert -list -v -alias <name_alias> -keystore <path_file_keystore>

With:

name_alias is name of alias when you create keystore
path_file_keystore is là path of file keystore

Ex: In project FluxStore (default build debug),

Find the name_alias in file android/key-debug.properties (keyAlias)

Find the path of file keystore in android/app/mstore.keystore

=> Command:

keytool -exportcert -list -v -alias mstoreapp -keystore android/app/mstore.keystore

Note: Must call the command at the project's root directory

Step 3: Open your project, remove file goole-services.json in folder **android/app**

Next, go back to firebase and download the file google-services.json. Save it to the android/app folder (instead of the recently delete google-services.json file)