Rails 4 + Omniauth + Devise: Logout link not working

Question

I'm using Omniauth as my only method for signing into my Rails application.

The issue is: When a user clicks "Logout", the page reloads and the Logout link is still there (despite if user_signed_in? logic wrapping it). Which leads me to believe that users aren't actually getting logged out

Here's my index.html.erb:

<% if user_signed_in? %>
  <%= link_to "Authenticate with Google", user_omniauth_authorize_path(:google_oauth2) %>
<% else %>
  <%= link_to('Logout', destroy_user_session_path, :method => :delete) %>
<% end %>

And my user.rb

def self.from_omniauth(auth)
  if user = User.find_by_email(auth.info.email)
    user.provider = auth.provider
    user.uid = auth.uid
    user
  else
    where(provider: auth.provider, uid: auth.uid).first_or_create do |user|
      user.provider = auth.provider
      user.uid = auth.uid
      user.email = auth.info.email # THIS (user.email) value i want to provide to my registration form as default value
   end
  end
end

And my omniauth_callbacks_controller.rb:

class OmniauthCallbacksController < Devise::OmniauthCallbacksController 
  skip_before_filter :redirect_to_login_if_required
  def google_oauth2
    @user = User.from_omniauth(request.env["omniauth.auth"])
    if @user.persisted?
      sign_in_and_redirect @user, :event => :authentication
      return
    else
      session["devise.user_attributes"] = @user.attributes
      redirect_to new_user_registration_path
    end
  end
end

And my routes.rb:

devise_for :users, :controllers => { :omniauth_callbacks => "omniauth_callbacks" }

Unfortunately it's not bringing me back an error. It's just refreshing the index page as if nothing happened.

Edit: Here's the POST when I click Logout

Started DELETE "/users/sign_out" for ::1 at 2015-07-06 11:00:22 -0400
Processing by Devise::SessionsController#destroy as HTML
  Parameters: {"authenticity_token"=>"7QXScU8eVW6NVedKG5P86rPxkaP8uJdUzyJ712ZrYXtK7QjP/m33eQ2WE/ituUvFQ2GeenXLRBaiVibxEjHG6w=="}
Redirected to http://localhost:3000/
Filter chain halted as :verify_signed_out_user rendered or redirected
Completed 302 Found in 1ms (ActiveRecord: 0.0ms)

Edit 2: I've included this in my application_controller.rb

before_action :authenticate_user!

And now the error message I'm getting in the console is:

Started GET "/users/auth/google_oauth2/callback?state=c92f3f9e0a8db79485e56ec2a1defd91949e8e7d99a02130&code=4/pgl_HZFw113L7VJ-rSaV9-JYngABkfgx7lqRm06Dyqg" for ::1 at 2015-07-06 16:12:14 -0400
I, [2015-07-06T16:12:14.739138 #2442]  INFO -- omniauth: (google_oauth2) Callback phase initiated.
Processing by OmniauthCallbacksController#google_oauth2 as HTML
  Parameters: {"state"=>"c92f3f9e0a8db79485e56ec2a1defd91949e8e7d99a02130", "code"=>"4/pgl_HZFw113L7VJ-rSaV9-JYngABkfgx7lqRm06Dyqg"}
  User Load (0.3ms)  SELECT  "users".* FROM "users" WHERE "users"."email" = ? LIMIT 1  [["email", "[email protected]"]]
   (0.1ms)  begin transaction
  SQL (0.4ms)  UPDATE "users" SET "last_sign_in_at" = ?, "current_sign_in_at" = ?, "sign_in_count" = ?, "updated_at" = ? WHERE "users"."id" = ?  [["last_sign_in_at", "2015-07-06 20:11:47.636852"], ["current_sign_in_at", "2015-07-06 20:12:15.365770"], ["sign_in_count", 42], ["updated_at", "2015-07-06 20:12:15.366734"], ["id", 4]]
   (1.4ms)  commit transaction
Redirected to http://localhost:3000/
Completed 302 Found in 15ms (ActiveRecord: 2.1ms)


Started GET "/" for ::1 at 2015-07-06 16:12:15 -0400
Processing by ProductlinesController#index as HTML
Completed 401 Unauthorized in 0ms (ActiveRecord: 0.0ms)