[Rails] Devise Omniauth + Vkontakte. When trying to login "Not found. Authentication passthru." What's the matter?

Question

Ruby on Rails

Hello!
I do authentication through VKontakte. I use gems devise, omniauth, omniauth-vkontakte.
When I click on the link to log in through VKontakte, a message-page appears ( localhost:8080/users/auth/vkontakte.user):
"Not found. Authentication passthru."
In the initialization of devise.rb : where 'APP_ID', 'APP_SECRET' are the values ​​obtained when registering the application on the VKontakte server , model user.rb :
config.omniauth :vkontakte, 'APP_ID', 'APP_SECRET'

devise :database_authenticatable, :registerable, :recoverable, :rememberable, :trackable, :validatable,
         :omniauthable, omniauth_providers: [:vkontakte]
  attr_accessor :email, :password, :password_confirmation, :remember_me
  attr_accessor :nickname, :provider, :url, :username         
 
  def self.find_for_vkontakte_oauth access_token
    if user = User.where(:url => access_token.info.urls.Vkontakte).first
      user
    else 
      User.create!(:provider => access_token.provider, :url => access_token.info.urls.Vkontakte, :username => access_token.info.name, :nickname => access_token.extra.raw_info.domain, :email => access_token.extra.raw_info.domain+'<hh user=vk>.com', :password => Devise.friendly_token[0,20]) 
    end
  end

controller users/ominiauth_callbacks_controller.rb :

class Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
  include Devise::Controllers::Rememberable
  
  def facebook
  end

  def vkontakte
    @user = User.find_for_vkontakte_oauth request.env["omniauth.auth"]
    if @user.persisted?
      remember_me(@user)
      flash[:notice] = I18n.t "devise.omniauth_callbacks.success", :kind => "Vkontakte"
      sign_in_and_redirect @user, :event => :authentication
    else
      flash[:notice] = "authentication error"
      redirect_to root_path
    end    
  end

  def passthru
    super    
  end
end

routes.rb :

devise_for :users, controllers: { omniauth_callbacks: "users/omniauth_callbacks" }

actually the link itself to log in through VKontakte:

<%- if devise_mapping.omniauthable? %>
  <%- resource_class.omniauth_providers.each do |provider| %>
    <%= link_to "Sign in with #{provider.to_s.titleize}", user_omniauth_authorize_path(resource_name, provider:provider) %><br />
  <% end -%>
<% end -%>

ruby '2.1.4'
rails '4.1.6'

Answer 1

Searching for quite a few answers on this issue. None fit?
Where they write that a restart must be done, where - that this is an omniaus legacy.
It seems that everything is correct, but:
1. What is the link localhost:8080/users/auth/vkontakte.user ? It usually looks like localhost:8080/users/auth/vkontakte
2. Why does a user have attr_accessories?
3. Why are you identifying the user by a link, and not by a pair of provider + uid ? People love to change nicknames
4. Is that a typo?
provider is passed as a parameter, not as part of the hash. I copied this from my working project:

link_to "Sign in with #{provider.to_s.titleize}", omniauth_authorize_path(resource_name, provider)