*[https://console.firebase.google.com/project/_/authentication/providers Firebase コンソール] で Googleサインインプロバイダーを有効化
*[https://pub.dev/packages/google_sign_in google_sign_in]
====iOS====
<pre>
<!-- Put me in the [my_project]/ios/Runner/Info.plist file -->
<!-- Google Sign-in Section -->
<key>CFBundleURLTypes</key>
<array>
<dict>
<key>CFBundleTypeRole</key>
<string>Editor</string>
<key>CFBundleURLSchemes</key>
<array>
<!-- TODO Replace this value: -->
<!-- Copied from GoogleService-Info.plist key REVERSED_CLIENT_ID -->
<string>com.googleusercontent.apps.861823949799-vc35cprkp249096uujjn0vvnmcvjppkn</string>
</array>
</dict>
</array>
<!-- End of the Google Sign-in Section -->
</pre>