Handle errors when fetching access token at callback phase

[ivan05almeida]

At the callback_phase if an error occurs on the fetch of the access_token the strategy is not handling the error.

Error Trace:

Rack::OAuth2::Client::Error (invalid_client :: invalid client credentials):
  rack-oauth2 (1.9.3) lib/rack/oauth2/client.rb:171:in `handle_error_response'
  rack-oauth2 (1.9.3) lib/rack/oauth2/client.rb:148:in `handle_response'
  rack-oauth2 (1.9.3) lib/rack/oauth2/client.rb:122:in `access_token!'
  /Users/coffeebean/Bitbucket/omniauth_openid_connect/lib/omniauth/strategies/openid_connect.rb:189:in `access_token'
  /Users/coffeebean/Bitbucket/omniauth_openid_connect/lib/omniauth/strategies/openid_connect.rb:114:in `callback_phase'
  omniauth (1.9.0) lib/omniauth/strategy.rb:238:in `callback_call'
  omniauth (1.9.0) lib/omniauth/strategy.rb:189:in `call!'
  omniauth (1.9.0) lib/omniauth/strategy.rb:169:in `call'
  exception_notification (4.3.0) lib/exception_notification/rack.rb:41:in `call'
  warden (1.2.7) lib/warden/manager.rb:36:in `block in call'
  warden (1.2.7) lib/warden/manager.rb:35:in `catch'
  warden (1.2.7) lib/warden/manager.rb:35:in `call'
  rack (1.6.11) lib/rack/etag.rb:24:in `call'
  rack (1.6.11) lib/rack/conditionalget.rb:25:in `call'
  rack (1.6.11) lib/rack/head.rb:13:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/flash.rb:260:in `call'
  rack (1.6.11) lib/rack/session/abstract/id.rb:225:in `context'
  rack (1.6.11) lib/rack/session/abstract/id.rb:220:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/cookies.rb:560:in `call'
  activerecord (4.2.11.1) lib/active_record/query_cache.rb:36:in `call'
  activerecord (4.2.11.1) lib/active_record/connection_adapters/abstract/connection_pool.rb:653:in `call'
  activerecord (4.2.11.1) lib/active_record/migration.rb:377:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
  activesupport (4.2.11.1) lib/active_support/callbacks.rb:88:in `__run_callbacks__'
  activesupport (4.2.11.1) lib/active_support/callbacks.rb:778:in `_run_call_callbacks'
  activesupport (4.2.11.1) lib/active_support/callbacks.rb:81:in `run_callbacks'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/reloader.rb:73:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/remote_ip.rb:78:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
  railties (4.2.11.1) lib/rails/rack/logger.rb:38:in `call_app'
  railties (4.2.11.1) lib/rails/rack/logger.rb:20:in `block in call'
  activesupport (4.2.11.1) lib/active_support/tagged_logging.rb:68:in `block in tagged'
  activesupport (4.2.11.1) lib/active_support/tagged_logging.rb:26:in `tagged'
  activesupport (4.2.11.1) lib/active_support/tagged_logging.rb:68:in `tagged'
  railties (4.2.11.1) lib/rails/rack/logger.rb:20:in `call'
  request_store (1.4.1) lib/request_store/middleware.rb:19:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/request_id.rb:21:in `call'
  rack (1.6.11) lib/rack/methodoverride.rb:22:in `call'
  rack (1.6.11) lib/rack/runtime.rb:18:in `call'
  activesupport (4.2.11.1) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
  rack (1.6.11) lib/rack/lock.rb:17:in `call'
  actionpack (4.2.11.1) lib/action_dispatch/middleware/static.rb:120:in `call'
  rack (1.6.11) lib/rack/sendfile.rb:113:in `call'
  railties (4.2.11.1) lib/rails/engine.rb:518:in `call'
  railties (4.2.11.1) lib/rails/application.rb:165:in `call'
  rack (1.6.11) lib/rack/content_length.rb:15:in `call'
  puma (3.12.0) lib/puma/configuration.rb:225:in `call'
  puma (3.12.0) lib/puma/server.rb:658:in `handle_request'
  puma (3.12.0) lib/puma/server.rb:472:in `process_client'
  puma (3.12.0) lib/puma/server.rb:332:in `block in run'
  puma (3.12.0) lib/puma/thread_pool.rb:133:in `block in spawn_thread'