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`lib/omniauth/strategies/google_id_token.rb`


# OmniAuth::GoogleIdToken

A [omnitauth](https://github.com/omniauth/omniauth) strategy primarily used for validating Google ID tokens
(JWT encoded) generated by Google authentication servers. As with other Omniauth strategies, it can also
redirect to Google's Sign In page.

As a validation strategy only this used by backend servers to validate Google ID tokens (Google
authenticated users) passed on by mobile or webapps e.g.
[ios](https://developers.google.com/identity/sign-in/ios/backend-auth),
[Android](https://developers.google.com/identity/sign-in/android/backend-auth),
[websites](https://developers.google.com/identity/sign-in/web/backend-auth).

This makes use of [google-id-token](https://github.com/google/google-id-token) for validating the ID token.

## Installation

Add this line to your application's Gemfile:

    gem 'omniauth-google-id-token'

And then execute:

    $ bundle

Or install it yourself as:

    $ gem install omniauth-google-id-token

## Usage

You use OmniAuth::Strategies::GoogleIdToken just like you do any other OmniAuth strategy:

```ruby
Rails.application.config.middleware.use OmniAuth::Builder do
  provider :developer, :callback_path => "/nexus-api/auth/developer/callback", provider_ignores_state: true if Rails.env.development?
  # provider :google-oauth2, ENV['GOOGLE_CLIENT_ID'], ENV['GOOGLE_CLIENT_SECRET'], scope: 'email, profile', provider_ignores_state: true , :callback_path => "/nexus-api/auth/google-oauth2/callback"
    
  
  provider :'google-id-token', client_id: ENV['GOOGLE_CLIENT_ID']
  # or
  # to rename the provider
  use OmniAuth::Strategies::GoogleIdToken,name: "google-oauth2",  client_id: ENV['GOOGLE_CLIENT_ID']
  
  
end

OmniAuth.config.allowed_request_methods = %i[get post]

```

If this strategy is used primarily for validating a Google ID token, then the only required fields are
aud_claim and azp_claim.

If this strategy is also used for redirecting a user to the Google Sign In page before validation,
then a client_id is also required. An example of the URL can be found at
https://developers.google.com/identity/protocols/OAuth2WebServer#handlingresponse Sample OAuth 2.0 server
response section.

* **name:** The name of the strategy. The default name is `google_id_token` but it can be changed to any value, for
  example `google`. The OmniAuth URL will thus change to `/auth/google` and the `provider` key in the auth hash will
  then return `google`.
* **uid_claim:** this determines which claim will be used to uniquely identify the user. Defaults
  to `sub`
* **client_id:** The client ID string that you obtain from the [API Console](https://console.developers.google.com/),
  as described in [Obtain OAuth 2.0 credentials](https://developers.google.com/identity/protocols/OpenIDConnect#getcredentials)
* **required_claims:** array of claims that are required to make this a valid authentication call.
  Defaults to `['name', 'email']`
* **scope:** array of request data in google api. Defaults to `['name', 'email', 'openid']`
* **info_map:** array mapping claim values to info hash values. Defaults to mapping `name` and `email`
  to the same in the info hash.

### Authentication Process

When you authenticate through `omniauth-google-id-token` you can send users to `/auth/google-id-token`
and it will redirect them to the URL https://accounts.google.com/o/oauth2/auth (and example can be
found at https://developers.google.com/identity/protocols/OAuth2WebServer#handlingresponse
Sample OAuth 2.0 server response).

From there, Google generates a ID token and sends to the redirect_uri passed in URL query params.
The redirect_uri will look like '/auth/google-id-token/callback`. This is the endpoint to send the id token
to if coming from a mobile or web app looking to validate a user with the backend server:

    /auth/google-id-token/callback?id_token=ENCODEDJWTGOESHERE

## Contributing

1. Fork it
2. Create your feature branch (`git checkout -b my-new-feature`)
3. Commit your changes (`git commit -am 'Add some feature'`)
4. Push to the branch (`git push origin my-new-feature`)
5. Create new Pull Request