Add basic HTTP client support

Author: jcat4

README.md

@@ -247,6 +247,24 @@ The HTTP client supports:
 - Tool invocation via the `tools/call` method
 - Automatic JSON-RPC 2.0 message formatting
 - UUID v7 request ID generation
+- Setting headers for things like authorization
+
+### HTTP Authorization
+
+By default, the HTTP client has no authentication, but it supports custom headers for authentication. For example, to use Bearer token authentication:
+
+```ruby
+client = ModelContextProtocol::Client::Http.new(
+  url: "https://api.example.com/mcp",
+  headers: {
+    "Authorization" => "Bearer my_token"
+  }
+)
+
+client.tools # will make the call using Bearer auth
+```
+
+You can add any custom headers needed for your authentication scheme. The client will include these headers in all requests.
 
 ### Tool Objects
 

lib/mcp/client/http.rb

@@ -7,9 +7,10 @@ class Http
 
       attr_reader :url, :version
 
-      def initialize(url:, version: DEFAULT_VERSION)
+      def initialize(url:, version: DEFAULT_VERSION, headers: {})
         @url = url
         @version = version
+        @headers = headers
       end
 
       def tools
@@ -29,12 +30,17 @@ def call_tool(tool:, input:)
 
       private
 
-      # TODO: support auth
+      attr_reader :headers
+
       def client
         @client ||= Faraday.new(url) do |faraday|
           faraday.request(:json)
           faraday.response(:json)
           faraday.response(:raise_error)
+
+          headers.each do |key, value|
+            faraday.headers[key] = value
+          end
         end
       end
 

test/model_context_protocol/client/http_test.rb

@@ -19,6 +19,39 @@ def test_initialization_with_custom_version
         assert_equal(custom_version, client.version)
       end
 
+      def test_headers_are_added_to_the_request
+        headers = { "Authorization" => "Bearer token" }
+        client = Http.new(url:, headers:)
+        client.stubs(:request_id).returns(mock_request_id)
+
+        stub_request(:post, url)
+          .with(
+            headers: {
+              "Authorization" => "Bearer token",
+              "Content-Type" => "application/json",
+            },
+            body: {
+              method: "tools/list",
+              jsonrpc: "2.0",
+              id: mock_request_id,
+              mcp: {
+                method: "tools/list",
+                jsonrpc: "2.0",
+                id: mock_request_id,
+              },
+            },
+          )
+          .to_return(
+            status: 200,
+            headers: { "Content-Type" => "application/json" },
+            body: { result: { tools: [] } }.to_json,
+          )
+
+        # The test passes if the request is made with the correct headers
+        # If headers are wrong, the stub_request won't match and will raise
+        client.tools
+      end
+
       def test_tools_returns_tools_instance
         stub_request(:post, url)
           .with(