Initializer if OmniAuth decides not to cooperate with your project when dealing with raised exceptions after unsuccessful login attempts

fix_omniauth.rb

# config/initializers/fix_omniauth.rb

begin
  require "omniauth"
  require "omniauth/version"
rescue LoadError => e
  warn "Could not load 'omniauth'. Please ensure you have the omniauth gem >= 1.0.0 installed and listed in your Gemfile."
  raise
end

# Clean up the default path_prefix. It will be automatically set by Devise.
OmniAuth.config.path_prefix = nil

OmniAuth.config.on_failure = Proc.new do |env|
  env['devise.mapping'] = Devise.mappings[:user]
  controller_name  = ActiveSupport::Inflector.camelize(env['devise.mapping'].controllers[:omniauth_callbacks])
  controller_klass = ActiveSupport::Inflector.constantize("#{controller_name}Controller")
  controller_klass.action(:failure).call(env)
end

module Devise
  module OmniAuth
    autoload :Config,      "devise/omniauth/config"
    autoload :UrlHelpers,  "devise/omniauth/url_helpers"
  end
end