http://ruby-ua.blogspot.com/2011/06/standalone-oauth-20-ruby-mechanize.html

0.rb

require 'oauth2'
require 'mechanize'

@client = OAuth2::Client.new(
  'client_id',
  'client_secret',
  :site          => 'https://api.vk.com/',
  :token_url     => '/oauth/token',
  :authorize_url => '/oauth/authorize' 
)

auth_url = @client.auth_code.authorize_url(
  :redirect_uri => 'http://api.vk.com/blank.html',
  :scope        => '',
  :display      => 'wap'
)

agent = Mechanize.new{|a| a.user_agent_alias = 'Linux Konqueror'}
login_page = agent.get(auth_url)

login_form = login_page.forms.first
login_form.email = 'email'
login_form.pass  = 'pass'

verify_page = login_form.submit

if verify_page.uri.path == '/oauth/authorize'
  if /m=4/.match(verify_page.uri.query)
    raise "Вказано невірний логін або пароль."
  elsif /s=1/.match(verify_page.uri.query)
    grant_access_page = verify_page.forms.first.submit
  end
else
  grant_access_page = verify_page
end

code = /code=(?<code>.*)/.match(grant_access_page.uri.fragment)['code']

@access_token = @client.auth_code.get_token(code)
@access_token.options[:param_name] = 'access_token'
@access_token.options[:mode] = :query

@access_token.get('/method/getProfiles', :params => {:uids => '1', :fields => 'city,country'}).parsed

1.rb

require 'oauth2'
require 'mechanize'

2.rb

@client = OAuth2::Client.new(
  'client_id',
  'client_secret',
  :site          => 'https://api.vk.com/',
  :token_url     => '/oauth/token',
  :authorize_url => '/oauth/authorize' 
)

3.rb

auth_url = @client.auth_code.authorize_url(
  :redirect_uri => 'http://api.vk.com/blank.html',
  :scope        => '',
  :display      => 'wap'
)

agent = Mechanize.new{|a| a.user_agent_alias = 'Linux Konqueror'}
login_page = agent.get(auth_url)

4.rb

login_form = login_page.forms.first
login_form.email = 'email'
login_form.pass  = 'pass'

verify_page = login_form.submit

5.rb

if verify_page.uri.path == '/oauth/authorize'
  if /m=4/.match(verify_page.uri.query)
    raise "Вказано невірний логін або пароль."
  elsif /s=1/.match(verify_page.uri.query)
    grant_access_page = verify_page.forms.first.submit
  end
else
  grant_access_page = verify_page
end

6.rb

code = /code=(?<code>.*)/.match(grant_access_page.uri.fragment)['code']

7.rb

@access_token = @client.auth_code.get_token(code)
@access_token.options[:param_name] = 'access_token'
@access_token.options[:mode] = :query

8.rb

@access_token.get('/method/getProfiles', :params => {:uids => '1', :fields => 'city,country'}).parsed