devise user sign_in gives authentication error for CSRF token authenticity token

I am using devise (latest version - 3.2.0) with rails (latest version - 4.0.1)

I'm doing simple authentication (without ajax or api) and getting an error for CSRF authenticity token. Check the POST request below

started POST "/users/sign_in" for 127.0.0.1 at 2013-11-08 19:48:49 +0530
Processing by Devise::SessionsController#create as HTML

 Parameters: {"utf8"=>"✓",    
 "authenticity_token"=>"SJnGhXXUXjncnPhCdg3muV2GYCA8CX2LVFV78pqddD4=", "user"=> 
{"email"=>"a@a.com", "password"=>"[FILTERED]", "remember_me"=>"0"},
"commit"=>"Sign in"}

Can't verify CSRF token authenticity
 User Load (0.4ms)  SELECT "users".* FROM "users" WHERE "users"."email" =  
'a@a.com' LIMIT 1
(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" = 2  [["last_sign_in_at", Fri,
08 Nov 2013 14:13:56 UTC +00:00], ["current_sign_in_at", Fri, 08 Nov 2013 14:18:49 UTC
+00:00], ["sign_in_count", 3], ["updated_at", Fri, 08 Nov 2013 14:18:49 UTC +00:00]]
(143.6ms)  commit transaction
Redirected to http://localhost:3000/
Completed 302 Found in 239ms (ActiveRecord: 144.5ms | Search: 0.0ms)

The root url points to home#new, which is like

class HomeController < ApplicationController
   before_action :authenticate_user!
   def index
   end
end

Sign_in page generated html view is like:

• meta tags

  <meta content="authenticity_token" name="csrf-param" />
  <meta content="aV+d7Z55XBJF2VtyL8V3zupR3OwhaQ6UHNtlQLBQf5Y=" name="csrf-token" />
  

• form

  <form accept-charset="UTF-8" action="/users/sign_in" class="new_user" id="new_user" 
  method="post">
  <div style="margin:0;padding:0;display:inline">
  <input name="utf8" type="hidden" value="&#x2713;" />
  <input name="authenticity_token" type="hidden
  value="aV+d7Z55XBJF2VtyL8V3zupR3OwhaQ6UHNtlQLBQf5Y=" />
  </div>
  <div><label for="user_email">Email</label><br />
  <input autofocus="autofocus" id="user_email" name="user[email]" type="email" value="" />
  </div>
  
  <div><label for="user_password">Password</label><br />
  <input id="user_password" name="user[password]" type="password" /></div>
  
  <div><input name="user[remember_me]" type="hidden" value="0" />
  <input id="user_remember_me" name="user[remember_me]" type="checkbox" value="1" /> 
  <label for="user_remember_me">Remember me</label></div>
  
  <div><input name="commit" type="submit" value="Sign in" /></div>
  </form>
  

The authentication request even updates the last_sign_in_at and sign_in_count values, but when I try to access current_user in controller it comes as nil.

According to me it is not actually signing in user. But then question comes "why it is updating last_sign_in_at/sign_in_count value in the user table ?"

There was no problem with devise gem . I removed 'rails-api' gem and my app started working.