Add support for RFC7797 unencoded payloads

.rubocop.yml

@@ -29,7 +29,7 @@ Metrics/AbcSize:
   Max: 25
 
 Metrics/ClassLength:
-  Max: 121
+  Max: 140
 
 Metrics/ModuleLength:
   Max: 100

README.md

@@ -680,6 +680,72 @@ jwk_hash = jwk.export
 thumbprint_as_the_kid = jwk_hash[:kid]
 ```
 
+### Unencoded and Detached Payloads
+
+#### Unencoded Payloads
+
+To generate a JWT with an unencoded payload, you may use the `b64` header set to false as described by RFC 7797. When you do this, the `crit` header will be added if it doesn't already exist, and the `b64` value will be appended to it.
+
+```ruby
+private_key = RbNaCl::Signatures::Ed25519::SigningKey.new('abcdefghijklmnopqrstuvwxyzABCDEF')
+public_key = private_key.verify_key
+token = JWT.encode payload, private_key, 'ED25519', { b64: false }
+
+# eyJiNjQiOmZhbHNlLCJhbGciOiJFRDI1NTE5IiwiY3JpdCI6WyJiNjQiXX0.{\"data\":\"test\"}.RL6jDz7h_fbQQds1x_ABOVE_dp646ZIbzvBB_DlixrTTMAiG7k0q4wH8dpcQ7KUeGgqI0tqj7B4JG_jTwM6fCg
+puts token
+
+decoded_token = JWT.decode token, public_key, true, { algorithm: 'ED25519' }
+# Array
+# [
+#  {"data"=>"test"}, # payload
+#  {"b64"=>false, "alg"=>"ED25519", "crit"=>["b64"]} # header
+# ]
+```
+
+It is extremely important that one take great care when using unencoded payloads, as the payload must be url safe if it is intended to be transmitted, etc. Also, because `.` is used to delineate between JWT segments, the payload must not have any `.` characters. If the paylod contains `.` then an `InvalidUnencodedPayload` error is raised.
+
+For the above reasons, detached payloads are often used in combination with unencoded payloads.
+
+#### Detached Payloads
+
+To generate a JWT with a detached payload, you must call `encode_detached` instead of `encode`. Then, when decoding and verifying the token, you must pass the `payload` option with the value of the detached payload before encoding.
+
+```ruby
+private_key = RbNaCl::Signatures::Ed25519::SigningKey.new('abcdefghijklmnopqrstuvwxyzABCDEF')
+public_key = private_key.verify_key
+token = JWT.encode_detached payload, private_key, 'ED25519'
+
+# eyJhbGciOiJFRDI1NTE5In0..6xIztXyOupskddGA_RvKU76V9b2dCQUYhoZEVFnRimJoPYIzZ2Fm47CWw8k2NTCNpgfAuxg9OXjaiVK7MvrbCQ
+puts token
+
+decoded_token = JWT.decode token, public_key, true, { algorithm: 'ED25519', payload: payload }
+# Array
+# [
+#  {"test"=>"data"}, # payload
+#  {"alg"=>"ED25519"} # header
+# ]
+```
+
+#### Combining Unencoded and Detached Payload Support
+
+Unencoded and detached payloads are often used hand in hand, such as in proof signatures of Verifiable Credentials. You may use the `b64` header in combination with `encode_detached` to combine both features.
+
+```ruby
+private_key = RbNaCl::Signatures::Ed25519::SigningKey.new('abcdefghijklmnopqrstuvwxyzABCDEF')
+public_key = private_key.verify_key
+token = JWT.encode_detached payload, private_key, 'ED25519', { b64: false }
+
+# eyJiNjQiOmZhbHNlLCJhbGciOiJFRDI1NTE5IiwiY3JpdCI6WyJiNjQiXX0..RL6jDz7h_fbQQds1x_ABOVE_dp646ZIbzvBB_DlixrTTMAiG7k0q4wH8dpcQ7KUeGgqI0tqj7B4JG_jTwM6fCg
+puts token
+
+decoded_token = JWT.decode token, public_key, true, { algorithm: 'ED25519', payload: payload }
+# Array
+# [
+#  {"data"=>"test"}, # payload
+#  {"b64"=>false, "alg"=>"ED25519", "crit"=>["b64"]} # header
+# ]
+```
+
 # Development and Tests
 
 We depend on [Bundler](http://rubygems.org/gems/bundler) for defining gemspec and performing releases to rubygems.org, which can be done with

lib/jwt.rb

@@ -22,7 +22,16 @@ def encode(payload, key, algorithm = 'HS256', header_fields = {})
     Encode.new(payload: payload,
                key: key,
                algorithm: algorithm,
-               headers: header_fields).segments
+               headers: header_fields,
+               detached: false).segments
+  end
+
+  def encode_detached(payload, key, algorithm = 'HS256', header_fields = {})
+    Encode.new(payload: payload,
+               key: key,
+               algorithm: algorithm,
+               headers: header_fields,
+               detached: true).segments
   end
 
   def decode(jwt, key = nil, verify = true, options = {}, &keyfinder) # rubocop:disable Style/OptionalBooleanParameter

lib/jwt/decode.rb

@@ -14,6 +14,7 @@ def initialize(jwt, key, verify, options, &keyfinder)
 
       @jwt = jwt
       @key = key
+      @detached_payload = options[:payload]
       @options = options
       @segments = jwt.split('.')
       @verify = verify
@@ -152,15 +153,35 @@ def header
     end
 
     def payload
-      @payload ||= parse_and_decode @segments[1]
+      @payload ||= parse_and_decode(encoded_payload, decode: decode_payload?)
+    end
+
+    def encoded_payload
+      payload = encoded_detached_payload if !@detached_payload.nil? && @segments[1].empty?
+      payload ||= @segments[1]
+      payload
+    end
+
+    def encoded_detached_payload
+      payload ||= ::JWT::Base64.url_encode(JWT::JSON.generate(@detached_payload)) if decode_payload?
+      payload ||= @detached_payload.to_json
+      payload
+    end
+
+    def decode_payload?
+      header['b64'].nil? || !!header['b64']
     end
 
     def signing_input
-      @segments.first(2).join('.')
+      [@segments[0], encoded_payload].join('.')
     end
 
-    def parse_and_decode(segment)
-      JWT::JSON.parse(::JWT::Base64.url_decode(segment))
+    def parse_and_decode(segment, decode: true)
+      if decode
+        JWT::JSON.parse(::JWT::Base64.url_decode(segment))
+      else
+        JWT::JSON.parse(segment)
+      end
     rescue ::JSON::ParserError
       raise JWT::DecodeError, 'Invalid segment encoding'
     end

lib/jwt/encode.rb

@@ -15,11 +15,24 @@ def initialize(options)
       @algorithm        = resolve_algorithm(options[:algorithm])
       @headers          = options[:headers].transform_keys(&:to_s)
       @headers[ALG_KEY] = @algorithm.alg
+      @detached         = options[:detached]
+
+      # add b64 claim to crit as per RFC7797 proposed standard
+      unless encode_payload?
+        @headers['crit'] ||= []
+        @headers['crit'] << 'b64' unless @headers['crit'].include?('b64')
+      end
     end
 
     def segments
       validate_claims!
-      combine(encoded_header_and_payload, encoded_signature)
+
+      parts = []
+      parts << encoded_header
+      parts << (@detached ? '' : encoded_payload)
+      parts << encoded_signature
+
+      combine(*parts)
     end
 
     private
@@ -51,7 +64,21 @@ def encode_header
     end
 
     def encode_payload
-      encode_data(@payload)
+      # if b64 header is present and false, do not encode payload as per RFC7797 proposed standard
+      encode_payload? ? encode_data(@payload) : prepare_unencoded_payload
+    end
+
+    def encode_payload?
+      # if b64 header is left out, default to true as per RFC7797 proposed standard
+      @headers['b64'].nil? || !!@headers['b64']
+    end
+
+    def prepare_unencoded_payload
+      json = @payload.to_json
+
+      raise(JWT::InvalidUnencodedPayload, 'An unencoded payload cannot contain period/dot characters (i.e. ".").') if json.include?('.')
+
+      json
     end
 
     def signature

lib/jwt/error.rb

@@ -5,6 +5,7 @@ class EncodeError < StandardError; end
   class DecodeError < StandardError; end
   class RequiredDependencyError < StandardError; end
 
+  class InvalidUnencodedPayload < EncodeError; end
   class VerificationError < DecodeError; end
   class ExpiredSignature < DecodeError; end
   class IncorrectAlgorithm < DecodeError; end

spec/jwt_spec.rb

@@ -2,6 +2,8 @@
 
 RSpec.describe JWT do
   let(:payload) { { 'user_id' => '[email protected]' } }
+  let(:unencoded_payload) { { 'user_id' => 'safe_value' } }
+  let(:unencoded_payload_unsafe) { { 'user_id' => 'unsafe.value' } }
 
   let :data do
     data = {
@@ -24,6 +26,9 @@
       'ES256K_public' => OpenSSL::PKey.read(File.read(File.join(CERT_PATH, 'ec256k-public.pem'))),
       'NONE' => 'eyJhbGciOiJub25lIn0.eyJ1c2VyX2lkIjoic29tZUB1c2VyLnRsZCJ9.',
       'HS256' => 'eyJhbGciOiJIUzI1NiJ9.eyJ1c2VyX2lkIjoic29tZUB1c2VyLnRsZCJ9.kWOVtIOpWcG7JnyJG0qOkTDbOy636XrrQhMm_8JrRQ8',
+      'HS256_unencoded_payload' => 'eyJiNjQiOmZhbHNlLCJhbGciOiJIUzI1NiIsImNyaXQiOlsiYjY0Il19.{"user_id":"safe_value"}.eW4NSHANyJpL6ivfFut7a5CM5lpaif8vEQYr-CRzrUc',
+      'HS256_detached_payload' => 'eyJhbGciOiJIUzI1NiJ9..oDy7wJe4wR3YcvGx5EmVm42H68g3L8nFfKnx3yeH25o',
+      'HS256_unencoded_detached_payload' => 'eyJiNjQiOmZhbHNlLCJhbGciOiJIUzI1NiIsImNyaXQiOlsiYjY0Il19..eW4NSHANyJpL6ivfFut7a5CM5lpaif8vEQYr-CRzrUc',
       'HS512256' => 'eyJhbGciOiJIUzUxMjI1NiJ9.eyJ1c2VyX2lkIjoic29tZUB1c2VyLnRsZCJ9.Ds_4ibvf7z4QOBoKntEjDfthy3WJ-3rKMspTEcHE2bA',
       'HS384' => 'eyJhbGciOiJIUzM4NCJ9.eyJ1c2VyX2lkIjoic29tZUB1c2VyLnRsZCJ9.VuV4j4A1HKhWxCNzEcwc9qVF3frrEu-BRLzvYPkbWO0LENRGy5dOiBQ34remM3XH',
       'HS512' => 'eyJhbGciOiJIUzUxMiJ9.eyJ1c2VyX2lkIjoic29tZUB1c2VyLnRsZCJ9.8zNtCBTJIZTHpZ-BkhR-6sZY1K85Nm5YCKqV3AxRdsBJDt_RR-REH2db4T3Y0uQwNknhrCnZGvhNHrvhDwV1kA',
@@ -933,4 +938,55 @@ def valid_alg?(alg)
       end
     end
   end
+
+  context 'when payload is not encoded' do
+    it 'should generate a valid token' do
+      token = JWT.encode unencoded_payload, data[:secret], 'HS256', { b64: false }
+
+      expect(token).to eq data['HS256_unencoded_payload']
+    end
+
+    it 'should decode a valid token' do
+      jwt_payload, header = JWT.decode data['HS256_unencoded_payload'], data[:secret], true, algorithm: 'HS256'
+
+      expect(header['alg']).to eq 'HS256'
+      expect(jwt_payload).to eq unencoded_payload
+    end
+
+    it 'should raise error when payload is unsafe for decoding' do
+      expect do
+        JWT.encode unencoded_payload_unsafe, 'secret', 'HS256', { b64: false }
+      end.to raise_error JWT::InvalidUnencodedPayload
+    end
+  end
+
+  context 'when payload is detached' do
+    it 'should generate a valid token' do
+      token = JWT.encode_detached unencoded_payload, data[:secret], 'HS256'
+
+      expect(token).to eq data['HS256_detached_payload']
+    end
+
+    it 'should decode a valid token' do
+      jwt_payload, header = JWT.decode data['HS256_detached_payload'], data[:secret], true, algorithm: 'HS256', payload: unencoded_payload
+
+      expect(header['alg']).to eq 'HS256'
+      expect(jwt_payload).to eq unencoded_payload
+    end
+  end
+
+  context 'when payload is unencoded and detached' do
+    it 'should generate a valid token' do
+      token = JWT.encode_detached unencoded_payload, data[:secret], 'HS256', { b64: false }
+
+      expect(token).to eq data['HS256_unencoded_detached_payload']
+    end
+
+    it 'should decode a valid token' do
+      jwt_payload, header = JWT.decode data['HS256_unencoded_detached_payload'], data[:secret], true, algorithm: 'HS256', payload: unencoded_payload
+
+      expect(header['alg']).to eq 'HS256'
+      expect(jwt_payload).to eq unencoded_payload
+    end
+  end
 end