feat(oauth): wire stdio OAuth 2.1 login into the server

Connect the internal/oauth core library to the stdio MCP server so users
can authenticate with an OAuth App or GitHub App client ID instead of a
static personal access token.

- BearerAuthTransport gains a TokenProvider that is consulted per request,
  letting the lazily-acquired, auto-refreshing OAuth token take effect
  without rebuilding the client.
- createGitHubClients uses BearerAuthTransport (and skips go-github's
  WithAuthToken, which would pin a static token) when a TokenProvider is set.
- RunStdioServer starts without a token and installs receiving middleware
  that runs the authorization flow on the first tool call, surfacing the
  auth URL or device code via elicitation (or a tool result as a fallback).
- Tool filtering uses the requested OAuth scopes; the default supported set
  hides nothing, while a narrower --oauth-scopes both narrows the grant and
  filters tools accordingly.
- A sessionPrompter adapts the MCP server session to oauth.Prompter, keeping
  the authorization URL off the model's context.
- New stdio flags: --oauth-client-id/-client-secret/-scopes/-callback-port.

This is stdio-only and deliberately does not touch MCP-HTTP auth.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: SamMorrowDrums

cmd/github-mcp-server/main.go

@@ -8,8 +8,10 @@ import (
 	"time"
 
 	"github.com/github/github-mcp-server/internal/ghmcp"
+	"github.com/github/github-mcp-server/internal/oauth"
 	"github.com/github/github-mcp-server/pkg/github"
 	ghhttp "github.com/github/github-mcp-server/pkg/http"
+	ghoauth "github.com/github/github-mcp-server/pkg/http/oauth"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
 	"github.com/spf13/viper"
@@ -34,8 +36,9 @@ var (
 		Long:  `Start a server that communicates via standard input/output streams using JSON-RPC messages.`,
 		RunE: func(_ *cobra.Command, _ []string) error {
 			token := viper.GetString("personal_access_token")
-			if token == "" {
-				return errors.New("GITHUB_PERSONAL_ACCESS_TOKEN not set")
+			oauthClientID := viper.GetString("oauth-client-id")
+			if token == "" && oauthClientID == "" {
+				return errors.New("authentication required: set GITHUB_PERSONAL_ACCESS_TOKEN, or pass --oauth-client-id to log in via OAuth")
 			}
 
 			// If you're wondering why we're not using viper.GetStringSlice("toolsets"),
@@ -95,6 +98,29 @@ var (
 				ExcludeTools:         excludeTools,
 				RepoAccessCacheTTL:   &ttl,
 			}
+
+			// When no static token is provided, log in via OAuth using the given
+			// client. The requested scopes default to the full supported set
+			// (which filters out no tools); an explicit, narrower --oauth-scopes
+			// both narrows the grant and hides tools needing other scopes.
+			if token == "" {
+				scopes := ghoauth.SupportedScopes
+				if viper.IsSet("oauth-scopes") {
+					if err := viper.UnmarshalKey("oauth-scopes", &scopes); err != nil {
+						return fmt.Errorf("failed to unmarshal oauth-scopes: %w", err)
+					}
+				}
+				oauthConfig := oauth.NewGitHubConfig(
+					oauthClientID,
+					viper.GetString("oauth-client-secret"),
+					scopes,
+					viper.GetString("host"),
+					viper.GetInt("oauth-callback-port"),
+				)
+				stdioServerConfig.OAuthManager = oauth.NewManager(oauthConfig, nil)
+				stdioServerConfig.OAuthScopes = scopes
+			}
+
 			return ghmcp.RunStdioServer(stdioServerConfig)
 		},
 	}
@@ -183,6 +209,14 @@ func init() {
 	rootCmd.PersistentFlags().Bool("insiders", false, "Enable insiders features")
 	rootCmd.PersistentFlags().Duration("repo-access-cache-ttl", 5*time.Minute, "Override the repo access cache TTL (e.g. 1m, 0s to disable)")
 
+	// stdio-specific OAuth flags. Provide --oauth-client-id (instead of a token)
+	// to log in via the browser-based OAuth flow on first use. Works for both
+	// OAuth Apps and GitHub Apps.
+	stdioCmd.Flags().String("oauth-client-id", "", "OAuth App or GitHub App client ID, enabling interactive OAuth login when no token is set")
+	stdioCmd.Flags().String("oauth-client-secret", "", "OAuth client secret, if the app requires one (it is a public, non-confidential credential for distributed clients)")
+	stdioCmd.Flags().StringSlice("oauth-scopes", nil, "Comma-separated OAuth scopes to request; also filters tools to those scopes. Defaults to the full supported set")
+	stdioCmd.Flags().Int("oauth-callback-port", 0, "Fixed local port for the OAuth callback server. Defaults to a random port; set a fixed port when mapping it through Docker")
+
 	// HTTP-specific flags
 	httpCmd.Flags().Int("port", 8082, "HTTP server port")
 	httpCmd.Flags().String("listen-host", "", "Host the HTTP server binds to (e.g. 127.0.0.1). Empty binds to all interfaces.")
@@ -205,6 +239,10 @@ func init() {
 	_ = viper.BindPFlag("lockdown-mode", rootCmd.PersistentFlags().Lookup("lockdown-mode"))
 	_ = viper.BindPFlag("insiders", rootCmd.PersistentFlags().Lookup("insiders"))
 	_ = viper.BindPFlag("repo-access-cache-ttl", rootCmd.PersistentFlags().Lookup("repo-access-cache-ttl"))
+	_ = viper.BindPFlag("oauth-client-id", stdioCmd.Flags().Lookup("oauth-client-id"))
+	_ = viper.BindPFlag("oauth-client-secret", stdioCmd.Flags().Lookup("oauth-client-secret"))
+	_ = viper.BindPFlag("oauth-scopes", stdioCmd.Flags().Lookup("oauth-scopes"))
+	_ = viper.BindPFlag("oauth-callback-port", stdioCmd.Flags().Lookup("oauth-callback-port"))
 	_ = viper.BindPFlag("port", httpCmd.Flags().Lookup("port"))
 	_ = viper.BindPFlag("listen-host", httpCmd.Flags().Lookup("listen-host"))
 	_ = viper.BindPFlag("base-url", httpCmd.Flags().Lookup("base-url"))

internal/ghmcp/oauth.go

@@ -0,0 +1,128 @@
+package ghmcp
+
+import (
+	"context"
+	"crypto/rand"
+	"fmt"
+	"log/slog"
+
+	"github.com/github/github-mcp-server/internal/oauth"
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+)
+
+// sessionPrompter adapts an MCP server session to oauth.Prompter, presenting
+// authorization prompts to the user via elicitation. Keeping the prompt on the
+// MCP control channel (rather than a tool result) keeps the authorization URL
+// and any session-bound state out of the model's context.
+type sessionPrompter struct {
+	session *mcp.ServerSession
+}
+
+// elicitationCaps returns the client's declared elicitation capabilities, or nil
+// if the client did not advertise any.
+func (p *sessionPrompter) elicitationCaps() *mcp.ElicitationCapabilities {
+	params := p.session.InitializeParams()
+	if params == nil || params.Capabilities == nil {
+		return nil
+	}
+	return params.Capabilities.Elicitation
+}
+
+// CanPromptURL reports whether the client supports URL-mode elicitation.
+func (p *sessionPrompter) CanPromptURL() bool {
+	caps := p.elicitationCaps()
+	return caps != nil && caps.URL != nil
+}
+
+// PromptURL presents the authorization URL via URL-mode elicitation and blocks
+// until the user acknowledges, declines, or ctx is done.
+func (p *sessionPrompter) PromptURL(ctx context.Context, prompt oauth.Prompt) error {
+	res, err := p.session.Elicit(ctx, &mcp.ElicitParams{
+		Mode:          "url",
+		Message:       prompt.Message,
+		URL:           prompt.URL,
+		ElicitationID: rand.Text(),
+	})
+	if err != nil {
+		return err
+	}
+	if res.Action != "accept" {
+		return oauth.ErrPromptDeclined
+	}
+	return nil
+}
+
+// CanPromptForm reports whether the client supports form-mode elicitation. The
+// SDK treats a client that advertises neither form nor URL capabilities as
+// supporting forms, for backward compatibility, so we mirror that here.
+func (p *sessionPrompter) CanPromptForm() bool {
+	caps := p.elicitationCaps()
+	if caps == nil {
+		return false
+	}
+	return caps.Form != nil || caps.URL == nil
+}
+
+// PromptForm presents a textual acknowledgement (used to display a device code
+// when URL elicitation is unavailable) and blocks until the user responds.
+func (p *sessionPrompter) PromptForm(ctx context.Context, prompt oauth.Prompt) error {
+	res, err := p.session.Elicit(ctx, &mcp.ElicitParams{
+		Mode:    "form",
+		Message: prompt.Message,
+	})
+	if err != nil {
+		return err
+	}
+	if res.Action != "accept" {
+		return oauth.ErrPromptDeclined
+	}
+	return nil
+}
+
+// oauthAuthenticator is the subset of *oauth.Manager that the middleware needs.
+// Depending on the interface (rather than the concrete manager) lets the
+// middleware be exercised with a deterministic fake, since driving the real
+// manager to its branches would require standing up live GitHub flows.
+type oauthAuthenticator interface {
+	HasToken() bool
+	Authenticate(ctx context.Context, prompter oauth.Prompter) (*oauth.Outcome, error)
+}
+
+// createOAuthMiddleware returns receiving middleware that authorizes the session
+// lazily, on the first tool call. Authorization is deferred until here (rather
+// than at startup) because the prompts depend on an initialized session whose
+// elicitation capabilities are known.
+//
+// When a token is already available the call proceeds untouched. Otherwise the
+// flow runs: secure channels (browser, URL elicitation) block until the token
+// arrives and then the call proceeds; the last-resort channel returns the
+// instruction to the user as a tool result and asks them to retry.
+func createOAuthMiddleware(mgr oauthAuthenticator, logger *slog.Logger) func(next mcp.MethodHandler) mcp.MethodHandler {
+	return func(next mcp.MethodHandler) mcp.MethodHandler {
+		return func(ctx context.Context, method string, request mcp.Request) (mcp.Result, error) {
+			if method != "tools/call" || mgr.HasToken() {
+				return next(ctx, method, request)
+			}
+
+			callReq, ok := request.(*mcp.CallToolRequest)
+			if !ok {
+				return next(ctx, method, request)
+			}
+
+			outcome, err := mgr.Authenticate(ctx, &sessionPrompter{session: callReq.Session})
+			if err != nil {
+				return nil, fmt.Errorf("github authorization failed: %w", err)
+			}
+			if outcome != nil && outcome.UserAction != nil {
+				logger.Info("surfacing github authorization instructions to user")
+				return &mcp.CallToolResult{
+					Content: []mcp.Content{&mcp.TextContent{Text: outcome.UserAction.Message}},
+				}, nil
+			}
+			return next(ctx, method, request)
+		}
+	}
+}
+
+// ensure sessionPrompter satisfies the Prompter contract.
+var _ oauth.Prompter = (*sessionPrompter)(nil)