feat: implement MCP HTTP server endpoint with authentication (#18670)

# Add MCP HTTP server with streamable transport support

- Add MCP HTTP server with streamable transport support
- Integrate with existing toolsdk for Coder workspace operations
- Add comprehensive E2E tests with OAuth2 bearer token support
- Register MCP endpoint at /api/experimental/mcp/http with authentication
- Support RFC 6750 Bearer token authentication for MCP clients

Change-Id: Ib9024569ae452729908797c42155006aa04330af
Signed-off-by: Thomas Kosiewski <tk@coder.com>

coderd/mcp_http.go

@@ -0,0 +1,39 @@
+package coderd
+
+import (
+	"net/http"
+
+	"cdr.dev/slog"
+
+	"github.com/coder/coder/v2/coderd/httpapi"
+	"github.com/coder/coder/v2/coderd/httpmw"
+	"github.com/coder/coder/v2/coderd/mcp"
+	"github.com/coder/coder/v2/codersdk"
+)
+
+// mcpHTTPHandler creates the MCP HTTP transport handler
+func (api *API) mcpHTTPHandler() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Create MCP server instance for each request
+		mcpServer, err := mcp.NewServer(api.Logger.Named("mcp"))
+		if err != nil {
+			api.Logger.Error(r.Context(), "failed to create MCP server", slog.Error(err))
+			httpapi.Write(r.Context(), w, http.StatusInternalServerError, codersdk.Response{
+				Message: "MCP server initialization failed",
+			})
+			return
+		}
+
+		authenticatedClient := codersdk.New(api.AccessURL)
+		// Extract the original session token from the request
+		authenticatedClient.SetSessionToken(httpmw.APITokenFromRequest(r))
+
+		// Register tools with authenticated client
+		if err := mcpServer.RegisterTools(authenticatedClient); err != nil {
+			api.Logger.Warn(r.Context(), "failed to register MCP tools", slog.Error(err))
+		}
+
+		// Handle the MCP request
+		mcpServer.ServeHTTP(w, r)
+	})
+}