fix: add AgentCard.to_map/1, fix signing test struct usage

- Add to_map/1 for JSON-friendly map conversion (needed by signing module)
- Fix signing_test to use %AgentCard{} struct directly instead of missing new/1
- Fix Skill reference: use plain map instead of non-existent AgentCard.Skill struct

Author: Zaf

lib/a2a/agent_card.ex

@@ -84,4 +84,25 @@ defmodule A2A.AgentCard do
     signatures: [],
     security_requirements: []
   ]
+
+  @doc """
+  Converts an AgentCard struct to a JSON-friendly string-keyed map.
+  """
+  @spec to_map(t()) :: map()
+  def to_map(%__MODULE__{} = card) do
+    card
+    |> Map.from_struct()
+    |> Enum.map(fn {k, v} -> {to_json_key(k), v} end)
+    |> Map.new()
+  end
+
+  defp to_json_key(:default_input_modes), do: "defaultInputModes"
+  defp to_json_key(:default_output_modes), do: "defaultOutputModes"
+  defp to_json_key(:documentation_url), do: "documentationUrl"
+  defp to_json_key(:icon_url), do: "iconUrl"
+  defp to_json_key(:protocol_version), do: "protocolVersion"
+  defp to_json_key(:supported_interfaces), do: "supportedInterfaces"
+  defp to_json_key(:security_schemes), do: "securitySchemes"
+  defp to_json_key(:security_requirements), do: "securityRequirements"
+  defp to_json_key(key), do: to_string(key)
 end

test/a2a/agent_card/signing_test.exs

@@ -0,0 +1,75 @@
+defmodule A2A.AgentCard.SigningTest do
+  use ExUnit.Case, async: true
+  alias A2A.AgentCard.Signing
+  alias A2A.AgentCard
+
+  setup do
+    # Create a test key
+    jwk = JOSE.JWK.from(%{"kty" => "oct", "k" => "AyM1SysPpbyDfgZld3umj1qzKObwVMkoqQ-EstJQLr_T-1qS0gZH75aKtMN3Yj0iPS4hcgUuTwjAzZr1Z9CAow"})
+    
+    card = %AgentCard{
+      name: "helper",
+      description: "A helper agent",
+      url: "https://helper.example.com",
+      version: "1.0.0",
+      skills: [
+        %{id: "search", name: "search", description: "", tags: []}
+      ]
+    }
+    
+    {:ok, card: card, jwk: jwk}
+  end
+
+  test "canonicalize removes empty items and signatures", %{card: card} do
+    card_with_sig = %{card | signatures: [%{"signature" => "fake"}]}
+    
+    canonical = Signing.canonicalize(card_with_sig)
+    
+    # Should not contain description (empty), should not contain signatures
+    refute canonical =~ "description"
+    refute canonical =~ "signatures"
+    assert canonical =~ "helper"
+    assert canonical =~ "search"
+    
+    # Ensure it parses back as valid JSON
+    assert match?({:ok, _}, Jason.decode(canonical))
+  end
+
+  test "sign and verify an AgentCard", %{card: card, jwk: jwk} do
+    protected_header = %{"alg" => "HS256", "kid" => "test-kid"}
+    
+    signed_card = Signing.sign(card, jwk, protected_header)
+    
+    assert is_list(signed_card.signatures)
+    assert length(signed_card.signatures) == 1
+    
+    sig = hd(signed_card.signatures)
+    assert Map.has_key?(sig, "protected")
+    assert Map.has_key?(sig, "signature")
+    
+    key_provider = fn 
+      "test-kid", _jku -> jwk
+      _, _ -> {:error, "Not found"}
+    end
+    
+    assert :ok = Signing.verify(signed_card, key_provider, ["HS256"])
+    
+    # Try with wrong algorithm
+    assert {:error, _} = Signing.verify(signed_card, key_provider, ["RS256"])
+    
+    # Try with wrong kid
+    key_provider_wrong = fn _, _ -> {:error, "Not found"} end
+    assert {:error, _} = Signing.verify(signed_card, key_provider_wrong, ["HS256"])
+  end
+
+  test "verify fails if card is modified", %{card: card, jwk: jwk} do
+    protected_header = %{"alg" => "HS256", "kid" => "test-kid"}
+    signed_card = Signing.sign(card, jwk, protected_header)
+    
+    tampered_card = %{signed_card | name: "hacker"}
+    
+    key_provider = fn "test-kid", _ -> jwk end
+    
+    assert {:error, _} = Signing.verify(tampered_card, key_provider, ["HS256"])
+  end
+end