Add support for ECDSA P-384 (#685)

## Motivation and Context

See
https://github.com/modelcontextprotocol/registry/issues/482#issuecomment-3436993157
for full details.

This adds ECDSA P-384 (a popular NIST approved curve) in addition to
Ed25519.

## How Has This Been Tested?

I have tested with a local deployment against `mcp.joelverhagen.com`.
Also, I have added significant tests.

## Breaking Changes

None. (hopefully)

## 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)
- [x] 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

## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->

@domdomegg and I spoke a bit about this on Discord:
https://discord.com/channels/1358869848138059966/1369487942862504016/1423710918180606052

---------

Co-authored-by: adam jones <domdomegg+git@gmail.com>

cmd/publisher/auth/common.go

@@ -3,7 +3,11 @@ package auth
 import (
 	"bytes"
 	"context"
+	"crypto/ecdsa"
 	"crypto/ed25519"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/sha512"
 	"encoding/hex"
 	"encoding/json"
 	"fmt"
@@ -12,12 +16,24 @@ import (
 	"time"
 )
 
+type CryptoAlgorithm string
+
+const (
+	AlgorithmEd25519 CryptoAlgorithm = "ed25519"
+
+	// ECDSA with NIST P-384 curve
+	// public key is in compressed format
+	// signature is in R || S format
+	AlgorithmECDSAP384 CryptoAlgorithm = "ecdsap384"
+)
+
 // CryptoProvider provides common functionality for DNS and HTTP authentication
 type CryptoProvider struct {
-	registryURL string
-	domain      string
-	hexSeed     string
-	authMethod  string
+	registryURL     string
+	domain          string
+	privateKey      string
+	cryptoAlgorithm CryptoAlgorithm
+	authMethod      string
 }
 
 // GetToken retrieves the registry JWT token using cryptographic authentication
@@ -26,31 +42,26 @@ func (c *CryptoProvider) GetToken(ctx context.Context) (string, error) {
 		return "", fmt.Errorf("%s domain is required", c.authMethod)
 	}
 
-	if c.hexSeed == "" {
-		return "", fmt.Errorf("%s private key (hex seed) is required", c.authMethod)
+	if c.privateKey == "" {
+		return "", fmt.Errorf("%s private key (hex) is required", c.authMethod)
 	}
 
-	// Decode hex seed to private key
-	seedBytes, err := hex.DecodeString(c.hexSeed)
+	// Decode private key from hex
+	privateKeyBytes, err := hex.DecodeString(c.privateKey)
 	if err != nil {
-		return "", fmt.Errorf("invalid hex seed format: %w", err)
+		return "", fmt.Errorf("invalid hex private key format: %w", err)
 	}
 
-	if len(seedBytes) != ed25519.SeedSize {
-		return "", fmt.Errorf("invalid seed length: expected %d bytes, got %d", ed25519.SeedSize, len(seedBytes))
-	}
-
-	privateKey := ed25519.NewKeyFromSeed(seedBytes)
-
 	// Generate current timestamp
 	timestamp := time.Now().UTC().Format(time.RFC3339)
-
-	// Sign the timestamp
-	signature := ed25519.Sign(privateKey, []byte(timestamp))
-	signedTimestamp := hex.EncodeToString(signature)
+	signedTimestamp, err := c.signMessage(privateKeyBytes, []byte(timestamp))
+	if err != nil {
+		return "", fmt.Errorf("failed to sign timestamp: %w", err)
+	}
+	signedTimestampHex := hex.EncodeToString(signedTimestamp)
 
 	// Exchange signature for registry token
-	registryToken, err := c.exchangeTokenForRegistry(ctx, c.domain, timestamp, signedTimestamp)
+	registryToken, err := c.exchangeTokenForRegistry(ctx, c.domain, timestamp, signedTimestampHex)
 	if err != nil {
 		return "", fmt.Errorf("failed to exchange %s signature: %w", c.authMethod, err)
 	}
@@ -58,6 +69,38 @@ func (c *CryptoProvider) GetToken(ctx context.Context) (string, error) {
 	return registryToken, nil
 }
 
+func (c *CryptoProvider) signMessage(privateKeyBytes []byte, message []byte) ([]byte, error) {
+	switch c.cryptoAlgorithm {
+	case AlgorithmEd25519:
+		if len(privateKeyBytes) != ed25519.SeedSize {
+			return nil, fmt.Errorf("invalid seed length: expected %d bytes, got %d", ed25519.SeedSize, len(privateKeyBytes))
+		}
+
+		privateKey := ed25519.NewKeyFromSeed(privateKeyBytes)
+		signature := ed25519.Sign(privateKey, message)
+		return signature, nil
+	case AlgorithmECDSAP384:
+		if len(privateKeyBytes) != 48 {
+			return nil, fmt.Errorf("invalid seed length for ECDSA P-384: expected 48 bytes, got %d", len(privateKeyBytes))
+		}
+
+		digest := sha512.Sum384(message)
+		curve := elliptic.P384()
+		privateKey, err := ecdsa.ParseRawPrivateKey(curve, privateKeyBytes)
+		if err != nil {
+			return nil, fmt.Errorf("failed to parse ECDSA private key: %w", err)
+		}
+		r, s, err := ecdsa.Sign(rand.Reader, privateKey, digest[:])
+		if err != nil {
+			return nil, fmt.Errorf("failed to sign message: %w", err)
+		}
+		signature := append(r.Bytes(), s.Bytes()...)
+		return signature, nil
+	default:
+		return nil, fmt.Errorf("unsupported crypto algorithm: %s", c.cryptoAlgorithm)
+	}
+}
+
 // NeedsLogin always returns false for cryptographic auth since no interactive login is needed
 func (c *CryptoProvider) NeedsLogin() bool {
 	return false

cmd/publisher/auth/dns.go

@@ -5,13 +5,14 @@ type DNSProvider struct {
 }
 
 // NewDNSProvider creates a new DNS-based auth provider
-func NewDNSProvider(registryURL, domain, hexSeed string) Provider {
+func NewDNSProvider(registryURL, domain, privateKey string, cryptoAlgorithm CryptoAlgorithm) Provider {
 	return &DNSProvider{
 		CryptoProvider: &CryptoProvider{
-			registryURL: registryURL,
-			domain:      domain,
-			hexSeed:     hexSeed,
-			authMethod:  "dns",
+			registryURL:     registryURL,
+			domain:          domain,
+			privateKey:      privateKey,
+			cryptoAlgorithm: cryptoAlgorithm,
+			authMethod:      "dns",
 		},
 	}
 }

cmd/publisher/auth/http.go

@@ -5,13 +5,14 @@ type HTTPProvider struct {
 }
 
 // NewHTTPProvider creates a new HTTP-based auth provider
-func NewHTTPProvider(registryURL, domain, hexSeed string) Provider {
+func NewHTTPProvider(registryURL, domain, privateKey string, cryptoAlgorithm CryptoAlgorithm) Provider {
 	return &HTTPProvider{
 		CryptoProvider: &CryptoProvider{
-			registryURL: registryURL,
-			domain:      domain,
-			hexSeed:     hexSeed,
-			authMethod:  "http",
+			registryURL:     registryURL,
+			domain:          domain,
+			privateKey:      privateKey,
+			cryptoAlgorithm: cryptoAlgorithm,
+			authMethod:      "http",
 		},
 	}
 }

cmd/publisher/commands/login.go

@@ -17,6 +17,21 @@ const (
 	TokenFileName      = ".mcp_publisher_token" //nolint:gosec // Not a credential, just a filename
 )
 
+type CryptoAlgorithm auth.CryptoAlgorithm
+
+func (c *CryptoAlgorithm) String() string {
+	return string(*c)
+}
+
+func (c *CryptoAlgorithm) Set(v string) error {
+	switch v {
+	case string(auth.AlgorithmEd25519), string(auth.AlgorithmECDSAP384):
+		*c = CryptoAlgorithm(v)
+		return nil
+	}
+	return fmt.Errorf("invalid algorithm: %q (allowed: ed25519, ecdsap384)", v)
+}
+
 func LoginCommand(args []string) error {
 	if len(args) < 1 {
 		return errors.New("authentication method required\n\nUsage: mcp-publisher login <method>\n\nMethods:\n  github        Interactive GitHub authentication\n  github-oidc   GitHub Actions OIDC authentication\n  dns           DNS-based authentication (requires --domain and --private-key)\n  http          HTTP-based authentication (requires --domain and --private-key)\n  none          Anonymous authentication (for testing)")
@@ -28,13 +43,15 @@ func LoginCommand(args []string) error {
 	loginFlags := flag.NewFlagSet("login", flag.ExitOnError)
 	var domain string
 	var privateKey string
+	var cryptoAlgorithm = CryptoAlgorithm(auth.AlgorithmEd25519)
 	var registryURL string
 
 	loginFlags.StringVar(&registryURL, "registry", DefaultRegistryURL, "Registry URL")
 
 	if method == "dns" || method == "http" {
 		loginFlags.StringVar(&domain, "domain", "", "Domain name")
-		loginFlags.StringVar(&privateKey, "private-key", "", "Private key (64-char hex)")
+		loginFlags.StringVar(&privateKey, "private-key", "", "Private key (hex)")
+		loginFlags.Var(&cryptoAlgorithm, "algorithm", "Cryptographic algorithm (ed25519, ecdsap384)")
 	}
 
 	if err := loginFlags.Parse(args[1:]); err != nil {
@@ -52,12 +69,12 @@ func LoginCommand(args []string) error {
 		if domain == "" || privateKey == "" {
 			return errors.New("dns authentication requires --domain and --private-key")
 		}
-		authProvider = auth.NewDNSProvider(registryURL, domain, privateKey)
+		authProvider = auth.NewDNSProvider(registryURL, domain, privateKey, auth.CryptoAlgorithm(cryptoAlgorithm))
 	case "http":
 		if domain == "" || privateKey == "" {
 			return errors.New("http authentication requires --domain and --private-key")
 		}
-		authProvider = auth.NewHTTPProvider(registryURL, domain, privateKey)
+		authProvider = auth.NewHTTPProvider(registryURL, domain, privateKey, auth.CryptoAlgorithm(cryptoAlgorithm))
 	case "none":
 		authProvider = auth.NewNoneProvider(registryURL)
 	default: