How to stub JWT server validation using Google OAuth2 and RSpec

00.rspec_stub_google_oauth2_token.rb

require 'google/apis/oauth2_v2'

shared_context 'stub_google_token_validation' do
  before do
    allow_any_instance_of(Google::Apis::Oauth2V2::Oauth2Service).to receive(:tokeninfo).and_return(
        Google::Apis::Oauth2V2::Tokeninfo.new email: 'your_fake_email_here@rspec.test',
                                              issued_to: Rails.application.secrets[:google_client_id],
                                              audience: Rails.application.secrets[:google_client_id]
    )
  end
end

auth_request_spec.rb

# example using rspec-rails and rspec-rails-swagger
require 'swagger_helper'

RSpec.describe 'Authentification', type: :request, capture_examples: true do
  path '/auth/google' do
    parameter :id_token, in: :query, type: :string, required: true

    post summary: "auth request using Google OAuth id_token", tags: ['auth'] do
      produces 'application/json'

      response 401, description: "id_token is invalid" do
        let(:id_token) { 'invalid' }
      end

      response 200, description: "id token is valid" do
        # we suppose it's valid
        let(:id_token) { 'eyJhbGciOiJSUzI1NiIsImtpZCI6ImE1NDFkNmVmMDIyZDc3YTIzMThmN2RkNjU3ZjI3NzkzMjAzYmVkNGEiLCJ0eXAiOiJKV1QifQ' }
        # let's stub the responses
        include_context 'stub_google_token_validation'
      end
    end
  end
end