-
Notifications
You must be signed in to change notification settings - Fork 2k
/
authenticity_token.rb
256 lines (223 loc) · 7.96 KB
/
authenticity_token.rb
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
# frozen_string_literal: true
require 'rack/protection'
require 'securerandom'
require 'openssl'
require 'base64'
module Rack
module Protection
##
# Prevented attack:: CSRF
# Supported browsers:: all
# More infos:: http://en.wikipedia.org/wiki/Cross-site_request_forgery
#
# This middleware only accepts requests other than <tt>GET</tt>,
# <tt>HEAD</tt>, <tt>OPTIONS</tt>, <tt>TRACE</tt> if their given access
# token matches the token included in the session.
#
# It checks the <tt>X-CSRF-Token</tt> header and the <tt>POST</tt> form
# data.
#
# It is not OOTB-compatible with the {rack-csrf}[https://rubygems.org/gems/rack_csrf] gem.
# For that, the following patch needs to be applied:
#
# Rack::Protection::AuthenticityToken.default_options(key: "csrf.token", authenticity_param: "_csrf")
#
# == Options
#
# [<tt>:authenticity_param</tt>] the name of the param that should contain
# the token on a request. Default value:
# <tt>"authenticity_token"</tt>
#
# [<tt>:key</tt>] the name of the param that should contain
# the token in the session. Default value:
# <tt>:csrf</tt>
#
# [<tt>:allow_if</tt>] a proc for custom allow/deny logic. Default value:
# <tt>nil</tt>
#
# == Example: Forms application
#
# To show what the AuthenticityToken does, this section includes a sample
# program which shows two forms. One with, and one without a CSRF token
# The one without CSRF token field will get a 403 Forbidden response.
#
# Install the gem, then run the program:
#
# gem install 'rack-protection'
# ruby server.rb
#
# Here is <tt>server.rb</tt>:
#
# require 'rack/protection'
# require 'rack/session'
#
# app = Rack::Builder.app do
# use Rack::Session::Cookie, secret: 'secret'
# use Rack::Protection::AuthenticityToken
#
# run -> (env) do
# [200, {}, [
# <<~EOS
# <!DOCTYPE html>
# <html lang="en">
# <head>
# <meta charset="UTF-8" />
# <title>rack-protection minimal example</title>
# </head>
# <body>
# <h1>Without Authenticity Token</h1>
# <p>This takes you to <tt>Forbidden</tt></p>
# <form action="" method="post">
# <input type="text" name="foo" />
# <input type="submit" />
# </form>
#
# <h1>With Authenticity Token</h1>
# <p>This successfully takes you to back to this form.</p>
# <form action="" method="post">
# <input type="hidden" name="authenticity_token" value="#{Rack::Protection::AuthenticityToken.token(env['rack.session'])}" />
# <input type="text" name="foo" />
# <input type="submit" />
# </form>
# </body>
# </html>
# EOS
# ]]
# end
# end
#
# Rack::Handler::WEBrick.run app
#
# == Example: Customize which POST parameter holds the token
#
# To customize the authenticity parameter for form data, use the
# <tt>:authenticity_param</tt> option:
# use Rack::Protection::AuthenticityToken, authenticity_param: 'your_token_param_name'
class AuthenticityToken < Base
TOKEN_LENGTH = 32
default_options authenticity_param: 'authenticity_token',
key: :csrf,
allow_if: nil
def self.token(session, path: nil, method: :post)
new(nil).mask_authenticity_token(session, path: path, method: method)
end
def self.random_token
SecureRandom.urlsafe_base64(TOKEN_LENGTH, padding: false)
end
def accepts?(env)
session = session(env)
set_token(session)
safe?(env) ||
valid_token?(env, env['HTTP_X_CSRF_TOKEN']) ||
valid_token?(env, Request.new(env).params[options[:authenticity_param]]) ||
options[:allow_if]&.call(env)
rescue StandardError
false
end
def mask_authenticity_token(session, path: nil, method: :post)
set_token(session)
token = if path && method
per_form_token(session, path, method)
else
global_token(session)
end
mask_token(token)
end
GLOBAL_TOKEN_IDENTIFIER = '!real_csrf_token'
private_constant :GLOBAL_TOKEN_IDENTIFIER
private
def set_token(session)
session[options[:key]] ||= self.class.random_token
end
# Checks the client's masked token to see if it matches the
# session token.
def valid_token?(env, token)
return false if token.nil? || !token.is_a?(String) || token.empty?
session = session(env)
begin
token = decode_token(token)
rescue ArgumentError # encoded_masked_token is invalid Base64
return false
end
# See if it's actually a masked token or not. We should be able
# to handle any unmasked tokens that we've issued without error.
if unmasked_token?(token)
compare_with_real_token(token, session)
elsif masked_token?(token)
token = unmask_token(token)
compare_with_global_token(token, session) ||
compare_with_real_token(token, session) ||
compare_with_per_form_token(token, session, Request.new(env))
else
false # Token is malformed
end
end
# Creates a masked version of the authenticity token that varies
# on each request. The masking is used to mitigate SSL attacks
# like BREACH.
def mask_token(token)
one_time_pad = SecureRandom.random_bytes(token.length)
encrypted_token = xor_byte_strings(one_time_pad, token)
masked_token = one_time_pad + encrypted_token
encode_token(masked_token)
end
# Essentially the inverse of +mask_token+.
def unmask_token(masked_token)
# Split the token into the one-time pad and the encrypted
# value and decrypt it
token_length = masked_token.length / 2
one_time_pad = masked_token[0...token_length]
encrypted_token = masked_token[token_length..]
xor_byte_strings(one_time_pad, encrypted_token)
end
def unmasked_token?(token)
token.length == TOKEN_LENGTH
end
def masked_token?(token)
token.length == TOKEN_LENGTH * 2
end
def compare_with_real_token(token, session)
secure_compare(token, real_token(session))
end
def compare_with_global_token(token, session)
secure_compare(token, global_token(session))
end
def compare_with_per_form_token(token, session, request)
secure_compare(token,
per_form_token(session, request.path.chomp('/'), request.request_method))
end
def real_token(session)
decode_token(session[options[:key]])
end
def global_token(session)
token_hmac(session, GLOBAL_TOKEN_IDENTIFIER)
end
def per_form_token(session, path, method)
token_hmac(session, "#{path}##{method.downcase}")
end
def encode_token(token)
Base64.urlsafe_encode64(token)
end
def decode_token(token)
Base64.urlsafe_decode64(token)
end
def token_hmac(session, identifier)
OpenSSL::HMAC.digest(
OpenSSL::Digest.new('SHA256'),
real_token(session),
identifier
)
end
def xor_byte_strings(s1, s2)
s2 = s2.dup
size = s1.bytesize
i = 0
while i < size
s2.setbyte(i, s1.getbyte(i) ^ s2.getbyte(i))
i += 1
end
s2
end
end
end
end