Add handling of Linked Data Signatures in payloads (#4687)

* Add handling of Linked Data Signatures in payloads

* Add a way to sign JSON, fix canonicalization of signature options

* Fix signatureValue encoding, send out signed JSON when distributing

* Add missing security context

2 files changed, 89 insertions, 2 deletions

diff --git a/spec/lib/activitypub/linked_data_signature_spec.rb b/spec/lib/activitypub/linked_data_signature_spec.rb
new file mode 100644
index 000000000..ee4b68028
--- /dev/null
+++ b/spec/lib/activitypub/linked_data_signature_spec.rb
@@ -0,0 +1,86 @@
+require 'rails_helper'
+
+RSpec.describe ActivityPub::LinkedDataSignature do
+  include JsonLdHelper
+
+  let!(:sender) { Fabricate(:account, uri: 'http://example.com/alice') }
+
+  let(:raw_json) do
+    {
+      '@context' => 'https://www.w3.org/ns/activitystreams',
+      'id' => 'http://example.com/hello-world',
+    }
+  end
+
+  let(:json) { raw_json.merge('signature' => signature) }
+
+  subject { described_class.new(json) }
+
+  describe '#verify_account!' do
+    context 'when signature matches' do
+      let(:raw_signature) do
+        {
+          'creator' => 'http://example.com/alice',
+          'created' => '2017-09-23T20:21:34Z',
+        }
+      end
+
+      let(:signature) { raw_signature.merge('type' => 'RsaSignature2017', 'signatureValue' => sign(sender, raw_signature, raw_json)) }
+
+      it 'returns creator' do
+        expect(subject.verify_account!).to eq sender
+      end
+    end
+
+    context 'when signature is missing' do
+      let(:signature) { nil }
+
+      it 'returns nil' do
+        expect(subject.verify_account!).to be_nil
+      end
+    end
+
+    context 'when signature is tampered' do
+      let(:raw_signature) do
+        {
+          'creator' => 'http://example.com/alice',
+          'created' => '2017-09-23T20:21:34Z',
+        }
+      end
+
+      let(:signature) { raw_signature.merge('type' => 'RsaSignature2017', 'signatureValue' => 's69F3mfddd99dGjmvjdjjs81e12jn121Gkm1') }
+
+      it 'returns nil' do
+        expect(subject.verify_account!).to be_nil
+      end
+    end
+  end
+
+  describe '#sign!' do
+    subject { described_class.new(raw_json).sign!(sender) }
+
+    it 'returns a hash' do
+      expect(subject).to be_a Hash
+    end
+
+    it 'contains signature context' do
+      expect(subject['@context']).to include('https://www.w3.org/ns/activitystreams', 'https://w3id.org/identity/v1')
+    end
+
+    it 'contains signature' do
+      expect(subject['signature']).to be_a Hash
+      expect(subject['signature']['signatureValue']).to be_present
+    end
+
+    it 'can be verified again' do
+      expect(described_class.new(subject).verify_account!).to eq sender
+    end
+  end
+
+  def sign(from_account, options, document)
+    options_hash   = Digest::SHA256.hexdigest(canonicalize(options.merge('@context' => ActivityPub::LinkedDataSignature::CONTEXT)))
+    document_hash  = Digest::SHA256.hexdigest(canonicalize(document))
+    to_be_verified = options_hash + document_hash
+    Base64.strict_encode64(from_account.keypair.sign(OpenSSL::Digest::SHA256.new, to_be_verified))
+  end
+end
diff --git a/spec/services/activitypub/process_collection_service_spec.rb b/spec/services/activitypub/process_collection_service_spec.rb
index 6486483f6..bf3bc82aa 100644
--- a/spec/services/activitypub/process_collection_service_spec.rb
+++ b/spec/services/activitypub/process_collection_service_spec.rb
@@ -1,9 +1,10 @@
 require 'rails_helper'
 
 RSpec.describe ActivityPub::ProcessCollectionService do
-  subject { ActivityPub::ProcessCollectionService.new }
+  subject { described_class.new }
 
   describe '#call' do
-    pending
+    context 'when actor is the sender'
+    context 'when actor differs from sender'
   end
 end