Allow server startup without token for future zero-config OAuth

- Remove hard error when no token/OAuth configured
- Server now starts with warning instead of failing
- OAuth flow attempted if configured, but failures don't block startup
- Tools will fail when called without auth, but server remains running
- Enables future zero-configuration with baked-in fallback OAuth app
- Clear warning messages guide users on authentication options
- Addresses comment 3765150847

Co-authored-by: SamMorrowDrums <4811358+SamMorrowDrums@users.noreply.github.com>

Author: Copilot

cmd/github-mcp-server/main.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"os"
 	"sort"
@@ -39,7 +38,7 @@ var (
 		RunE: func(cmd *cobra.Command, _ []string) error {
 			token := viper.GetString("personal_access_token")
 
-			// If no token provided, check if OAuth is configured
+			// If no token provided, attempt OAuth if configured
 			if token == "" {
 				oauthClientID := viper.GetString("oauth_client_id")
 				if oauthClientID != "" {
@@ -54,12 +53,20 @@ var (
 
 					result, err := oauth.StartOAuthFlow(cmd.Context(), oauthCfg)
 					if err != nil {
-						return fmt.Errorf("OAuth flow failed: %w", err)
+						// OAuth flow failed - warn but allow server to start
+						// This enables future zero-configuration fallback patterns
+						fmt.Fprintf(os.Stderr, "Warning: OAuth flow failed: %v\n", err)
+						fmt.Fprintf(os.Stderr, "Starting server without authentication - tools will fail until authenticated\n")
+					} else {
+						token = result.AccessToken
 					}
-
-					token = result.AccessToken
 				} else {
-					return errors.New("GITHUB_PERSONAL_ACCESS_TOKEN not set and OAuth not configured (set --oauth-client-id or GITHUB_OAUTH_CLIENT_ID)")
+					// No token and no OAuth configured - warn but allow server to start
+					// This enables future zero-configuration use with baked-in fallback app
+					fmt.Fprintf(os.Stderr, "Warning: No authentication configured\n")
+					fmt.Fprintf(os.Stderr, "  - Set GITHUB_PERSONAL_ACCESS_TOKEN environment variable, or\n")
+					fmt.Fprintf(os.Stderr, "  - Configure OAuth with --oauth-client-id (or GITHUB_OAUTH_CLIENT_ID)\n")
+					fmt.Fprintf(os.Stderr, "Starting server without authentication - tools will fail until authenticated\n")
 				}
 			}