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
|
require 'openssl'
module OmniAuth
module Facebook
class SignedRequest
class UnknownSignatureAlgorithmError < NotImplementedError; end
SUPPORTED_ALGORITHM = 'HMAC-SHA256'
attr_reader :value, :secret
def self.parse(value, secret)
new(value, secret).payload
end
def initialize(value, secret)
@value = value
@secret = secret
end
def payload
@payload ||= parse_signed_request
end
private
def parse_signed_request
signature, encoded_payload = value.split('.')
return if signature.nil?
decoded_hex_signature = base64_decode_url(signature)
decoded_payload = JSON.parse(base64_decode_url(encoded_payload))
unless decoded_payload['algorithm'] == SUPPORTED_ALGORITHM
raise UnknownSignatureAlgorithmError, "unknown algorithm: #{decoded_payload['algorithm']}"
end
if valid_signature?(decoded_hex_signature, encoded_payload)
decoded_payload
end
end
def valid_signature?(signature, payload, algorithm = OpenSSL::Digest::SHA256.new)
OpenSSL::HMAC.digest(algorithm, secret, payload) == signature
end
def base64_decode_url(value)
value += '=' * (4 - value.size.modulo(4))
Base64.decode64(value.tr('-_', '+/'))
end
end
end
end
|
