1 files changed, 116 insertions, 0 deletions

diff --git a/internal/auth/credentials.go b/internal/auth/credentials.go
new file mode 100644
index 0000000..c558653
--- /dev/null
+++ b/internal/auth/credentials.go
@@ -0,0 +1,116 @@
+package auth
+
+import (
+        "context"
+        "crypto/sha256"
+        "encoding/base64"
+        "encoding/json"
+        "fmt"
+        "time"
+
+        "northwest.io/muxstr/internal/nostr"
+)
+
+// NostrCredentials implements credentials.PerRPCCredentials for NIP-98 authentication.
+// It automatically signs each gRPC request with a Nostr event (kind 27235) and
+// attaches it to the Authorization header.
+type NostrCredentials struct {
+        key            *nostr.Key
+        includePayload bool
+}
+
+// NewNostrCredentials creates credentials using the provided key.
+// Each RPC call will be authenticated with a freshly signed NIP-98 event.
+// The key must have a private key (CanSign() must return true).
+func NewNostrCredentials(key *nostr.Key) *NostrCredentials {
+        return &NostrCredentials{
+                key:            key,
+                includePayload: false,
+        }
+}
+
+// NewNostrCredentialsWithPayload creates credentials that include payload hashes.
+// When enabled, a SHA256 hash of the request body is included in the auth event.
+func NewNostrCredentialsWithPayload(key *nostr.Key) *NostrCredentials {
+        return &NostrCredentials{
+                key:            key,
+                includePayload: true,
+        }
+}
+
+// GetRequestMetadata implements credentials.PerRPCCredentials.
+// It creates and signs a NIP-98 auth event for each request.
+func (n *NostrCredentials) GetRequestMetadata(ctx context.Context, uri ...string) (map[string]string, error) {
+        if len(uri) == 0 {
+                return nil, fmt.Errorf("no URI provided")
+        }
+
+        // Create kind 27235 event (NIP-98 HTTP Auth)
+        event := &nostr.Event{
+                PubKey:    n.key.Public(),
+                CreatedAt: time.Now().Unix(),
+                Kind:      27235, // NIP-98 HTTP Auth
+                Tags:      nostr.Tags{},
+                Content:   "",
+        }
+
+        // Add URL tag
+        event.Tags = append(event.Tags, nostr.Tag{"u", uri[0]})
+
+        // Add method tag - default to POST for gRPC
+        // The URI contains the method name, e.g., /nostr.v1.NostrRelay/PublishEvent
+        event.Tags = append(event.Tags, nostr.Tag{"method", "POST"})
+
+        // TODO: Add payload hash if includePayload is true
+        // This requires access to the request body, which isn't available in GetRequestMetadata
+        // We could use a context key to pass the payload hash from the application
+
+        // Sign the event
+        if err := n.key.Sign(event); err != nil {
+                return nil, fmt.Errorf("failed to sign auth event: %w", err)
+        }
+
+        // Encode event as base64 JSON
+        eventJSON, err := json.Marshal(event)
+        if err != nil {
+                return nil, fmt.Errorf("failed to marshal auth event: %w", err)
+        }
+
+        authHeader := "Nostr " + base64.StdEncoding.EncodeToString(eventJSON)
+
+        return map[string]string{
+                "authorization": authHeader,
+        }, nil
+}
+
+// RequireTransportSecurity implements credentials.PerRPCCredentials.
+// Returns false to allow usage over insecure connections (for development).
+// In production, use TLS and set this to true.
+func (n *NostrCredentials) RequireTransportSecurity() bool {
+        return false
+}
+
+// SetRequireTLS configures whether TLS is required.
+// When true, the credentials will only work over TLS connections.
+type NostrCredentialsWithTLS struct {
+        *NostrCredentials
+}
+
+// NewNostrCredentialsWithTLS creates credentials that require TLS.
+func NewNostrCredentialsWithTLS(key *nostr.Key) *NostrCredentialsWithTLS {
+        return &NostrCredentialsWithTLS{
+                NostrCredentials: NewNostrCredentials(key),
+        }
+}
+
+// RequireTransportSecurity returns true to enforce TLS.
+func (n *NostrCredentialsWithTLS) RequireTransportSecurity() bool {
+        return true
+}
+
+// HashPayload creates a SHA256 hash of the payload for inclusion in auth events.
+// This can be used to verify request integrity.
+func HashPayload(payload []byte) string {
+        hash := sha256.Sum256(payload)
+        return fmt.Sprintf("%x", hash)
+}