feat: Add creds for GitHub auth, add "none" auth to publisher (#276)

## Motivation and Context

- Adds credentials for the new MCP Registry Login GitHub Apps (local,
staging, prod)
- Adds support for "none" auth to publisher

## How Has This Been Tested?

- Tested publisher workflows locally
- Unit and integration tests passing

## Breaking Changes

None

## 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)
- [x] 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. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

---

Merging based on Tadas's approval review, and only making minor docs changes on top of that.

tools/publisher/auth/none/none.go

@@ -0,0 +1,78 @@
+package none
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+
+	"github.com/modelcontextprotocol/registry/tools/publisher/auth"
+)
+
+type Provider struct {
+	registryURL string
+	token       string
+}
+
+type TokenResponse struct {
+	RegistryToken string `json:"registry_token"`
+	ExpiresAt     int64  `json:"expires_at"`
+}
+
+func NewProvider(registryURL string) auth.Provider { //nolint:ireturn
+	return &Provider{
+		registryURL: registryURL,
+	}
+}
+
+func (p *Provider) GetToken(ctx context.Context) (string, error) {
+	if p.token != "" {
+		return p.token, nil
+	}
+
+	// Get anonymous token from registry
+	if !strings.HasSuffix(p.registryURL, "/") {
+		p.registryURL += "/"
+	}
+	tokenURL := p.registryURL + "v0/auth/none"
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, tokenURL, nil)
+	if err != nil {
+		return "", fmt.Errorf("error creating request: %w", err)
+	}
+
+	client := &http.Client{}
+	resp, err := client.Do(req)
+	if err != nil {
+		return "", fmt.Errorf("error getting anonymous token: %w", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		body, _ := io.ReadAll(resp.Body)
+		return "", fmt.Errorf("failed to get anonymous token (status %d): %s", resp.StatusCode, body)
+	}
+
+	var tokenResp TokenResponse
+	if err := json.NewDecoder(resp.Body).Decode(&tokenResp); err != nil {
+		return "", fmt.Errorf("error decoding token response: %w", err)
+	}
+
+	p.token = tokenResp.RegistryToken
+	return p.token, nil
+}
+
+func (p *Provider) NeedsLogin() bool {
+	return false
+}
+
+func (p *Provider) Login(_ context.Context) error {
+	// No login needed for anonymous auth
+	return nil
+}
+
+func (p *Provider) Name() string {
+	return "none"
+}