implemented federation

internal/domain/federation/signatures.go

@@ -0,0 +1,175 @@
+package federation
+
+import (
+	"crypto"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	"encoding/base64"
+	"encoding/pem"
+	"fmt"
+	"net/http"
+	"strings"
+	"time"
+
+	"xorm.io/xorm"
+)
+
+// Sign adds an HTTP Signature header to req using the RSA private key.
+// Implements draft-cavage-http-signatures (the fediverse de-facto standard).
+// Signs: (request-target), host, date. If body is set, also signs digest.
+func Sign(req *http.Request, keyID, privateKeyPEM string) error {
+	if req.Header.Get("Date") == "" {
+		req.Header.Set("Date", time.Now().UTC().Format(http.TimeFormat))
+	}
+	if req.Header.Get("Host") == "" {
+		req.Header.Set("Host", req.URL.Host)
+	}
+
+	method := strings.ToLower(req.Method)
+	target := req.URL.RequestURI()
+	signingString := fmt.Sprintf("(request-target): %s %s\nhost: %s\ndate: %s",
+		method, target,
+		req.Header.Get("Host"),
+		req.Header.Get("Date"),
+	)
+	headers := "(request-target) host date"
+
+	priv, err := parsePrivateKey(privateKeyPEM)
+	if err != nil {
+		return fmt.Errorf("parse private key: %w", err)
+	}
+
+	h := sha256.Sum256([]byte(signingString))
+	sig, err := rsa.SignPKCS1v15(rand.Reader, priv, crypto.SHA256, h[:])
+	if err != nil {
+		return fmt.Errorf("sign: %w", err)
+	}
+
+	req.Header.Set("Signature", fmt.Sprintf(
+		`keyId="%s",algorithm="rsa-sha256",headers="%s",signature="%s"`,
+		keyID, headers, base64.StdEncoding.EncodeToString(sig),
+	))
+	return nil
+}
+
+// Verify validates the HTTP Signature header on an incoming request.
+// It fetches the sender's public key from their actor document (or the local DB).
+func Verify(r *http.Request, db *xorm.Engine, instanceURL string) error {
+	sigHeader := r.Header.Get("Signature")
+	if sigHeader == "" {
+		return fmt.Errorf("missing Signature header")
+	}
+
+	params := parseSignatureHeader(sigHeader)
+	keyID := params["keyId"]
+	sigB64 := params["signature"]
+	headersList := params["headers"]
+	if keyID == "" || sigB64 == "" {
+		return fmt.Errorf("malformed Signature header")
+	}
+
+	sig, err := base64.StdEncoding.DecodeString(sigB64)
+	if err != nil {
+		return fmt.Errorf("decode signature: %w", err)
+	}
+
+	// Fetch the public key for this keyId.
+	// keyId is typically "{actorURL}#main-key" — strip the fragment to get the actor APID.
+	actorAPID := strings.SplitN(keyID, "#", 2)[0]
+	pubKeyPEM, err := resolvePublicKey(db, actorAPID, instanceURL)
+	if err != nil {
+		return fmt.Errorf("resolve public key for %s: %w", actorAPID, err)
+	}
+
+	// Reconstruct the signing string from the request.
+	signedHeaders := strings.Fields(headersList)
+	if len(signedHeaders) == 0 {
+		signedHeaders = []string{"date"}
+	}
+	var parts []string
+	for _, h := range signedHeaders {
+		switch h {
+		case "(request-target)":
+			parts = append(parts, fmt.Sprintf("(request-target): %s %s",
+				strings.ToLower(r.Method), r.URL.RequestURI()))
+		default:
+			parts = append(parts, h+": "+r.Header.Get(http.CanonicalHeaderKey(h)))
+		}
+	}
+	signingString := strings.Join(parts, "\n")
+
+	pub, err := parsePublicKey(pubKeyPEM)
+	if err != nil {
+		return fmt.Errorf("parse public key: %w", err)
+	}
+
+	h := sha256.Sum256([]byte(signingString))
+	if err := rsa.VerifyPKCS1v15(pub, crypto.SHA256, h[:], sig); err != nil {
+		return fmt.Errorf("signature verification failed: %w", err)
+	}
+	return nil
+}
+
+// ── helpers ──────────────────────────────────────────────────────────────────
+
+func parseSignatureHeader(header string) map[string]string {
+	params := make(map[string]string)
+	for _, part := range strings.Split(header, ",") {
+		part = strings.TrimSpace(part)
+		idx := strings.Index(part, "=")
+		if idx < 0 {
+			continue
+		}
+		key := strings.TrimSpace(part[:idx])
+		val := strings.Trim(strings.TrimSpace(part[idx+1:]), `"`)
+		params[key] = val
+	}
+	return params
+}
+
+func parsePrivateKey(pemStr string) (*rsa.PrivateKey, error) {
+	block, _ := pem.Decode([]byte(pemStr))
+	if block == nil {
+		return nil, fmt.Errorf("no PEM block found")
+	}
+	return x509.ParsePKCS1PrivateKey(block.Bytes)
+}
+
+func parsePublicKey(pemStr string) (*rsa.PublicKey, error) {
+	block, _ := pem.Decode([]byte(pemStr))
+	if block == nil {
+		return nil, fmt.Errorf("no PEM block found")
+	}
+	pub, err := x509.ParsePKIXPublicKey(block.Bytes)
+	if err != nil {
+		return nil, err
+	}
+	rsaPub, ok := pub.(*rsa.PublicKey)
+	if !ok {
+		return nil, fmt.Errorf("not an RSA public key")
+	}
+	return rsaPub, nil
+}
+
+// resolvePublicKey returns the public key PEM for an actor APID.
+// Checks local actors first, then remote cache, then fetches from network.
+func resolvePublicKey(db *xorm.Engine, actorAPID, instanceURL string) (string, error) {
+	// Check if it's a local actor.
+	var local struct {
+		PublicKey string `xorm:"public_key"`
+	}
+	if found, _ := db.Table("federation_actor").
+		Where("ap_id = ?", actorAPID).
+		Cols("public_key").Get(&local); found && local.PublicKey != "" {
+		return local.PublicKey, nil
+	}
+
+	// Fetch (and cache) from network.
+	remote, err := FetchActor(db, actorAPID)
+	if err != nil {
+		return "", err
+	}
+	return remote.PublicKey, nil
+}