Extract Workhorse <-> GitLab authentication to make it reusable

Introduce JWTAutheticatable module that can be reused for ai=uthtication
between Pages and GitLab (the same way we use do now for Workhorse).

Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/61927.

2 files changed, 93 insertions, 51 deletions

diff --git a/spec/lib/gitlab/jwt_authenticatable_spec.rb b/spec/lib/gitlab/jwt_authenticatable_spec.rb
new file mode 100644
index 00000000000..0c1c491b308
--- /dev/null
+++ b/spec/lib/gitlab/jwt_authenticatable_spec.rb
@@ -0,0 +1,93 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::JwtAuthenticatable do
+  let(:test_class) do
+    Class.new do
+      include Gitlab::JwtAuthenticatable
+
+      def self.secret_path
+        Rails.root.join('tmp', 'tests', '.jwt_shared_secret')
+      end
+    end
+  end
+
+  before do
+    begin
+      File.delete(test_class.secret_path)
+    rescue Errno::ENOENT
+    end
+
+    test_class.write_secret
+  end
+
+  describe '.secret' do
+    subject(:secret) { test_class.secret }
+
+    it 'returns 32 bytes' do
+      expect(secret).to be_a(String)
+      expect(secret.length).to eq(32)
+      expect(secret.encoding).to eq(Encoding::ASCII_8BIT)
+    end
+
+    it 'accepts a trailing newline' do
+      File.open(test_class.secret_path, 'a') { |f| f.write "\n" }
+
+      expect(secret.length).to eq(32)
+    end
+
+    it 'raises an exception if the secret file cannot be read' do
+      File.delete(test_class.secret_path)
+
+      expect { secret }.to raise_exception(Errno::ENOENT)
+    end
+
+    it 'raises an exception if the secret file contains the wrong number of bytes' do
+      File.truncate(test_class.secret_path, 0)
+
+      expect { secret }.to raise_exception(RuntimeError)
+    end
+  end
+
+  describe '.write_secret' do
+    it 'uses mode 0600' do
+      expect(File.stat(test_class.secret_path).mode & 0777).to eq(0600)
+    end
+
+    it 'writes base64 data' do
+      bytes = Base64.strict_decode64(File.read(test_class.secret_path))
+
+      expect(bytes).not_to be_empty
+    end
+  end
+
+  describe '.decode_jwt_for_issuer' do
+    let(:payload) { { 'iss' => 'test_issuer' } }
+
+    it 'accepts a correct header' do
+      encoded_message = JWT.encode(payload, test_class.secret, 'HS256')
+
+      expect { test_class.decode_jwt_for_issuer('test_issuer', encoded_message) }.not_to raise_error
+    end
+
+    it 'raises an error when the JWT is not signed' do
+      encoded_message = JWT.encode(payload, nil, 'none')
+
+      expect { test_class.decode_jwt_for_issuer('test_issuer', encoded_message) }.to raise_error(JWT::DecodeError)
+    end
+
+    it 'raises an error when the header is signed with the wrong secret' do
+      encoded_message = JWT.encode(payload, 'wrongsecret', 'HS256')
+
+      expect { test_class.decode_jwt_for_issuer('test_issuer', encoded_message) }.to raise_error(JWT::DecodeError)
+    end
+
+    it 'raises an error when the issuer is incorrect' do
+      payload['iss'] = 'somebody else'
+      encoded_message = JWT.encode(payload, test_class.secret, 'HS256')
+
+      expect { test_class.decode_jwt_for_issuer('test_issuer', encoded_message) }.to raise_error(JWT::DecodeError)
+    end
+  end
+end
diff --git a/spec/lib/gitlab/workhorse_spec.rb b/spec/lib/gitlab/workhorse_spec.rb
index 98421cd12d3..88bc5034da5 100644
--- a/spec/lib/gitlab/workhorse_spec.rb
+++ b/spec/lib/gitlab/workhorse_spec.rb
@@ -200,57 +200,6 @@ describe Gitlab::Workhorse do
     end
   end
 
-  describe ".secret" do
-    subject { described_class.secret }
-
-    before do
-      described_class.instance_variable_set(:@secret, nil)
-      described_class.write_secret
-    end
-
-    it 'returns 32 bytes' do
-      expect(subject).to be_a(String)
-      expect(subject.length).to eq(32)
-      expect(subject.encoding).to eq(Encoding::ASCII_8BIT)
-    end
-
-    it 'accepts a trailing newline' do
-      File.open(described_class.secret_path, 'a') { |f| f.write "\n" }
-      expect(subject.length).to eq(32)
-    end
-
-    it 'raises an exception if the secret file cannot be read' do
-      File.delete(described_class.secret_path)
-      expect { subject }.to raise_exception(Errno::ENOENT)
-    end
-
-    it 'raises an exception if the secret file contains the wrong number of bytes' do
-      File.truncate(described_class.secret_path, 0)
-      expect { subject }.to raise_exception(RuntimeError)
-    end
-  end
-
-  describe ".write_secret" do
-    let(:secret_path) { described_class.secret_path }
-    before do
-      begin
-        File.delete(secret_path)
-      rescue Errno::ENOENT
-      end
-
-      described_class.write_secret
-    end
-
-    it 'uses mode 0600' do
-      expect(File.stat(secret_path).mode & 0777).to eq(0600)
-    end
-
-    it 'writes base64 data' do
-      bytes = Base64.strict_decode64(File.read(secret_path))
-      expect(bytes).not_to be_empty
-    end
-  end
-
   describe '#verify_api_request!' do
     let(:header_key) { described_class::INTERNAL_API_REQUEST_HEADER }
     let(:payload) { { 'iss' => 'gitlab-workhorse' } }