Implement --token and MCP_GITHUB_TOKEN login support (#705)

<!-- Provide a brief summary of your changes -->

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
The following PR implements the missing support for logging in via
`--token` or `MCP_GITHUB_TOKEN`

## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->

## Breaking Changes
<!-- Will users need to update their code or configurations? -->

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed

## Additional context
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-->
Fixes: #698

---------

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

cmd/publisher/auth/github-at.go

@@ -50,9 +50,10 @@ type StoredRegistryToken struct {
 
 // GitHubATProvider implements the Provider interface using GitHub's device flow
 type GitHubATProvider struct {
-	clientID    string
-	forceLogin  bool
-	registryURL string
+	clientID      string
+	forceLogin    bool
+	registryURL   string
+	providedToken string // Token provided via --token flag or MCP_GITHUB_TOKEN env var
 }
 
 // ServerHealthResponse represents the response from the health endpoint
@@ -62,10 +63,16 @@ type ServerHealthResponse struct {
 }
 
 // NewGitHubATProvider creates a new GitHub OAuth provider
-func NewGitHubATProvider(forceLogin bool, registryURL string) Provider {
+func NewGitHubATProvider(forceLogin bool, registryURL, token string) Provider {
+	// Check for token from flag or environment variable
+	if token == "" {
+		token = os.Getenv("MCP_GITHUB_TOKEN")
+	}
+
 	return &GitHubATProvider{
-		forceLogin:  forceLogin,
-		registryURL: registryURL,
+		forceLogin:    forceLogin,
+		registryURL:   registryURL,
+		providedToken: token,
 	}
 }
 
@@ -100,6 +107,11 @@ func (g *GitHubATProvider) GetToken(ctx context.Context) (string, error) {
 
 // NeedsLogin checks if a new login is required
 func (g *GitHubATProvider) NeedsLogin() bool {
+	// If a token was provided via --token or MCP_GITHUB_TOKEN, no login needed
+	if g.providedToken != "" {
+		return false
+	}
+
 	if g.forceLogin {
 		return true
 	}
@@ -123,6 +135,15 @@ func (g *GitHubATProvider) NeedsLogin() bool {
 
 // Login performs the GitHub device flow authentication
 func (g *GitHubATProvider) Login(ctx context.Context) error {
+	// If a token was provided via --token or MCP_GITHUB_TOKEN, save it and skip device flow
+	if g.providedToken != "" {
+		err := saveToken(g.providedToken)
+		if err != nil {
+			return fmt.Errorf("error saving provided token: %w", err)
+		}
+		return nil
+	}
+
 	// If clientID is not set, try to retrieve it from the server's health endpoint
 	if g.clientID == "" {
 		clientID, err := getClientID(ctx, g.registryURL)

cmd/publisher/commands/init.go

@@ -29,7 +29,7 @@ func InitCommand() error {
 	description := detectDescription()
 	version := "1.0.0"
 	repoURL := detectRepoURL()
-	repoSource := "github"
+	repoSource := MethodGitHub
 	if repoURL != "" && !strings.Contains(repoURL, "github.com") {
 		if strings.Contains(repoURL, "gitlab.com") {
 			repoSource = "gitlab"

cmd/publisher/commands/login.go

@@ -18,6 +18,11 @@ import (
 const (
 	DefaultRegistryURL = "https://registry.modelcontextprotocol.io"
 	TokenFileName      = ".mcp_publisher_token" //nolint:gosec // Not a credential, just a filename
+	MethodGitHub       = "github"
+	MethodGitHubOIDC   = "github-oidc"
+	MethodDNS          = "dns"
+	MethodHTTP         = "http"
+	MethodNone         = "none"
 )
 
 type CryptoAlgorithm auth.CryptoAlgorithm
@@ -31,6 +36,7 @@ type LoginFlags struct {
 	KvVault         string
 	KvKeyName       string
 	KmsResource     string
+	Token           Token
 	CryptoAlgorithm CryptoAlgorithm
 	SignerType      SignerType
 	ArgOffset       int
@@ -56,6 +62,8 @@ func (c *CryptoAlgorithm) Set(v string) error {
 	return fmt.Errorf("invalid algorithm: %q (allowed: ed25519, ecdsap384)", v)
 }
 
+type Token string
+
 func parseLoginFlags(method string, args []string) (LoginFlags, error) {
 	var flags LoginFlags
 	loginFlags := flag.NewFlagSet("login", flag.ExitOnError)
@@ -64,6 +72,12 @@ func parseLoginFlags(method string, args []string) (LoginFlags, error) {
 	flags.ArgOffset = 1
 	loginFlags.StringVar(&flags.RegistryURL, "registry", DefaultRegistryURL, "Registry URL")
 
+	// Add --token flag for GitHub authentication
+	var token string
+	if method == MethodGitHub {
+		loginFlags.StringVar(&token, "token", "", "GitHub Personal Access Token")
+	}
+
 	if method == "dns" || method == "http" {
 		loginFlags.StringVar(&flags.Domain, "domain", "", "Domain name")
 		if len(args) > 1 {
@@ -90,6 +104,11 @@ func parseLoginFlags(method string, args []string) (LoginFlags, error) {
 		flags.RegistryURL = strings.TrimRight(flags.RegistryURL, "/")
 	}
 
+	// Store the token in flags if it was provided
+	if method == MethodGitHub {
+		flags.Token = Token(token)
+	}
+
 	return flags, err
 }
 
@@ -108,23 +127,23 @@ func createSigner(flags LoginFlags) (auth.Signer, error) {
 	}
 }
 
-func createAuthProvider(method, registryURL, domain string, signer auth.Signer) (auth.Provider, error) {
+func createAuthProvider(method, registryURL, domain string, token Token, signer auth.Signer) (auth.Provider, error) {
 	switch method {
-	case "github":
-		return auth.NewGitHubATProvider(true, registryURL), nil
-	case "github-oidc":
+	case MethodGitHub:
+		return auth.NewGitHubATProvider(true, registryURL, string(token)), nil
+	case MethodGitHubOIDC:
 		return auth.NewGitHubOIDCProvider(registryURL), nil
-	case "dns":
+	case MethodDNS:
 		if domain == "" {
 			return nil, errors.New("dns authentication requires --domain")
 		}
 		return auth.NewDNSProvider(registryURL, domain, &signer), nil
-	case "http":
+	case MethodHTTP:
 		if domain == "" {
 			return nil, errors.New("http authentication requires --domain")
 		}
 		return auth.NewHTTPProvider(registryURL, domain, &signer), nil
-	case "none":
+	case MethodNone:
 		return auth.NewNoneProvider(registryURL), nil
 	default:
 		return nil, fmt.Errorf("unknown authentication method: %s\nFor a list of available methods, run: mcp-publisher login", method)
@@ -191,11 +210,10 @@ Examples:
 		}
 	}
 
-	authProvider, err := createAuthProvider(method, flags.RegistryURL, flags.Domain, signer)
+	authProvider, err := createAuthProvider(method, flags.RegistryURL, flags.Domain, flags.Token, signer)
 	if err != nil {
 		return err
 	}
-
 	ctx := context.Background()
 	_, _ = fmt.Fprintf(os.Stdout, "Logging in with %s...\n", method)