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Enhancement: Allow some protocol methods to bypass authentication #6

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Merged
merged 1 commit into from
Aug 22, 2025
Merged

Enhancement: Allow some protocol methods to bypass authentication #6

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33 changes: 31 additions & 2 deletions cmd/mcp-http/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ import (
"os"
"os/signal"
"regexp"
"slices"
"strings"
"syscall"
"time"
Expand Down Expand Up @@ -173,13 +174,41 @@ func tracerMiddleware(resources config.Resources, next http.Handler) http.Handle
}

func authMiddleware(resources config.Resources, next http.Handler) http.Handler {
whitelistEndpoints := map[string][]string{
// health checks don't require authentication
"/api/health": {http.MethodGet, http.MethodOptions},

// allow some protocol methods to bypass authentication
//
// https://modelcontextprotocol.io/specification/2025-06-18/basic/lifecycle
// https://modelcontextprotocol.io/specification/2025-06-18/server/tools#listing-tools
// https://modelcontextprotocol.io/specification/2025-06-18/server/resources#listing-resources
// https://modelcontextprotocol.io/specification/2025-06-18/server/resources#resource-templates
// https://modelcontextprotocol.io/specification/2025-06-18/server/prompts#listing-prompts
"/": {http.MethodPost},
"/tools/list": {http.MethodPost},
"/resources/list": {http.MethodPost},
"/resources/templates/list": {http.MethodPost},
"/prompts/list": {http.MethodPost},
}

whitelistPrefixEndpoints := map[string][]string{
// OAuth2 endpoints cannot require authentication
"/.well-known": {"GET", "OPTIONS"},
}

return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
// some endpoints don't require auth
if (r.URL.Path == "/api/health" || strings.HasPrefix(r.URL.Path, "/.well-known")) &&
(r.Method == http.MethodGet || r.Method == http.MethodOptions) {
if methods, ok := whitelistEndpoints[r.URL.Path]; ok && slices.Contains(methods, r.Method) {
next.ServeHTTP(w, r)
return
}
for prefix, methods := range whitelistPrefixEndpoints {
if strings.HasPrefix(r.URL.Path, prefix) && slices.Contains(methods, r.Method) {
next.ServeHTTP(w, r)
return
}
}

requestLogger := resources.Logger().With(
slog.String("method", r.Method),
Expand Down
103 changes: 80 additions & 23 deletions cmd/mcp-stdio/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ import (
"fmt"
"log/slog"
"os"
"slices"
"strings"

"github.com/mark3labs/mcp-go/mcp"
Expand All @@ -20,7 +21,23 @@ import (
)

var (
methods = methodsInput([]toolsets.Method{toolsets.MethodAll})
methods = methodsInput([]toolsets.Method{toolsets.MethodAll})
methodsWhitelist = []string{
// allow some protocol methods to bypass authentication
//
// https://modelcontextprotocol.io/specification/2025-06-18/basic/lifecycle
// https://modelcontextprotocol.io/specification/2025-06-18/server/tools#listing-tools
// https://modelcontextprotocol.io/specification/2025-06-18/server/resources#listing-resources
// https://modelcontextprotocol.io/specification/2025-06-18/server/resources#resource-templates
// https://modelcontextprotocol.io/specification/2025-06-18/server/prompts#listing-prompts
"initialize",
"notifications/initialized",
"logging/setLevel",
"tools/list",
"resources/list",
"resources/templates/list",
"prompts/list",
}
readOnly bool
)

Expand All @@ -34,33 +51,31 @@ func main() {
flag.BoolVar(&readOnly, "read-only", false, "Restrict the server to read-only operations")
flag.Parse()

if resources.Info.BearerToken == "" {
mcpError(resources, errors.New("TW_MCP_BEARER_TOKEN environment variable is not set"), mcp.INVALID_PARAMS)
exit(exitCodeSetupFailure)
}

ctx := context.Background()

// detect the installation from the bearer token
info, err := auth.GetBearerInfo(ctx, resources, resources.Info.BearerToken)
if err != nil {
mcpError(resources, fmt.Errorf("failed to authenticate: %s", err), mcp.INVALID_PARAMS)
exit(exitCodeSetupFailure)
}
if resources.Info.BearerToken != "" {
// detect the installation from the bearer token
info, err := auth.GetBearerInfo(ctx, resources, resources.Info.BearerToken)
if err != nil {
mcpError(resources.Logger(), fmt.Errorf("failed to authenticate: %s", err), mcp.INVALID_PARAMS)
exit(exitCodeSetupFailure)
}

// inject customer URL in the context
ctx = config.WithCustomerURL(ctx, info.URL)
// inject bearer token in the context
ctx = session.WithBearerTokenContext(ctx, session.NewBearerToken(resources.Info.BearerToken, info.URL))
// inject customer URL in the context
ctx = config.WithCustomerURL(ctx, info.URL)
// inject bearer token in the context
ctx = session.WithBearerTokenContext(ctx, session.NewBearerToken(resources.Info.BearerToken, info.URL))
}

mcpServer, err := newMCPServer(resources)
if err != nil {
mcpError(resources, fmt.Errorf("failed to create MCP server: %s", err), mcp.INTERNAL_ERROR)
mcpError(resources.Logger(), fmt.Errorf("failed to create MCP server: %s", err), mcp.INTERNAL_ERROR)
exit(exitCodeSetupFailure)
}
mcpSTDIOServer := server.NewStdioServer(mcpServer)
if err := mcpSTDIOServer.Listen(ctx, os.Stdin, os.Stdout); err != nil {
mcpError(resources, fmt.Errorf("failed to serve: %s", err), mcp.INTERNAL_ERROR)
stdinWrapper := newStdinWrapper(resources.Logger(), resources.Info.BearerToken != "", methodsWhitelist)
if err := mcpSTDIOServer.Listen(ctx, stdinWrapper, os.Stdout); err != nil {
mcpError(resources.Logger(), fmt.Errorf("failed to serve: %s", err), mcp.INTERNAL_ERROR)
exit(exitCodeSetupFailure)
}
}
Expand All @@ -73,14 +88,16 @@ func newMCPServer(resources config.Resources) (*server.MCPServer, error) {
return config.NewMCPServer(resources, group), nil
}

func mcpError(resources config.Resources, err error, code int) {
func mcpError(logger *slog.Logger, err error, code int) {
mcpError := mcp.NewJSONRPCError(mcp.NewRequestId("startup"), code, err.Error(), nil)
encoder := json.NewEncoder(os.Stdout)
if err := encoder.Encode(mcpError); err != nil {
resources.Logger().Error("failed to encode error",
encoded, err := json.Marshal(mcpError)
if err != nil {
logger.Error("failed to encode error",
slog.String("error", err.Error()),
)
return
}
fmt.Printf("%s\n", string(encoded))
}

type methodsInput []toolsets.Method
Expand Down Expand Up @@ -110,6 +127,46 @@ func (t *methodsInput) Set(value string) error {
return errs
}

type stdinWrapper struct {
logger *slog.Logger
authenticated bool
methodsWhitelist []string
}

func newStdinWrapper(logger *slog.Logger, authenticated bool, methods []string) stdinWrapper {
return stdinWrapper{
logger: logger,
authenticated: authenticated,
methodsWhitelist: methods,
}
}

func (s stdinWrapper) Read(p []byte) (n int, err error) {
if s.authenticated {
return os.Stdin.Read(p)
}
buffer := make([]byte, len(p))
n, err = os.Stdin.Read(buffer)
if err != nil {
return n, err
}
content := buffer[:n]
if len(content) == 0 {
return n, err
}
var baseMessage struct {
Method string `json:"method"`
}
if err := json.Unmarshal(content, &baseMessage); err != nil {
return 0, errors.New("parse error")
}
if !slices.Contains(s.methodsWhitelist, baseMessage.Method) {
return 0, errors.New("not authenticated")
}
copy(p, buffer)
return n, err
}

type exitCode int

const (
Expand Down