Improvement/encode hmac without key

README.md

@@ -79,6 +79,21 @@ puts token
 
 decoded_token = JWT.decode token, hmac_secret, true, { algorithm: 'HS256' }
 
+# Array
+# [
+#   {"data"=>"test"}, # payload
+#   {"alg"=>"HS256"} # header
+# ]
+puts decoded_token
+
+# Without secret key
+token = JWT.encode payload, nil, 'HS256'
+
+# eyJhbGciOiJIUzI1NiJ9.eyJkYXRhIjoidGVzdCJ9.pVzcY2dX8JNM3LzIYeP2B1e1Wcpt1K3TWVvIYSF4x-o
+puts token
+
+decoded_token = JWT.decode token, nil, true, { algorithm: 'HS256' }
+
 # Array
 # [
 #   {"data"=>"test"}, # payload
@@ -460,7 +475,7 @@ begin
 rescue JWT::JWKError
   # Handle problems with the provided JWKs
 rescue JWT::DecodeError
-  # Handle other decode related issues e.g. no kid in header, no matching public key found etc. 
+  # Handle other decode related issues e.g. no kid in header, no matching public key found etc.
 end
 ```
 

lib/jwt/algos/hmac.rb

@@ -7,6 +7,7 @@ module Hmac
 
       def sign(to_sign)
         algorithm, msg, key = to_sign.values
+        key ||= ''
         authenticator, padded_key = SecurityUtils.rbnacl_fixup(algorithm, key)
         if authenticator && padded_key
           authenticator.auth(padded_key, msg.encode('binary'))

spec/integration/readme_examples_spec.rb

@@ -18,7 +18,7 @@
       ]
     end
 
-    it 'HMAC' do
+    it 'decodes with HMAC algorithm with secret key' do
       token = JWT.encode payload, 'my$ecretK3y', 'HS256'
       decoded_token = JWT.decode token, 'my$ecretK3y', false
 
@@ -29,6 +29,17 @@
       ]
     end
 
+    it 'decodes with HMAC algorithm without secret key' do
+      token = JWT.encode payload, nil, 'HS256'
+      decoded_token = JWT.decode token, nil, false
+
+      expect(token).to eq 'eyJhbGciOiJIUzI1NiJ9.eyJkYXRhIjoidGVzdCJ9.pVzcY2dX8JNM3LzIYeP2B1e1Wcpt1K3TWVvIYSF4x-o'
+      expect(decoded_token).to eq [
+        { 'data' => 'test' },
+        { 'alg' => 'HS256' }
+      ]
+    end
+
     it 'RSA' do
       rsa_private = OpenSSL::PKey::RSA.generate 2048
       rsa_public = rsa_private.public_key

spec/jwt_spec.rb

@@ -404,4 +404,17 @@
       expect(JWT.encode('Hello World', 'secret', 'HS256', { alg: 'HS256'})).to eq JWT.encode('Hello World', 'secret', 'HS256')
     end
   end
+
+  context 'when hmac algorithm is used without secret key' do
+    it 'encodes payload' do
+      payload = { a: 1, b: 'b'}
+
+      token = JWT.encode(payload, '', 'HS256')
+
+      expect do
+        token_without_secret = JWT.encode(payload, nil, 'HS256')
+        expect(token).to eq(token_without_secret)
+      end.not_to raise_error
+    end
+  end
 end