Implemented API endpoint to sign arbitrary data

internal/security/signer.go

@@ -1,15 +1,18 @@
 package security
 
 import (
-	"context"
 	"crypto"
 	"crypto/rand"
 	"crypto/rsa"
 	"crypto/sha1"
-	"encoding/base64"
+	"crypto/x509"
+	"encoding/pem"
+	"errors"
+	"io"
 )
 
 var randomReader = rand.Reader
+var invalidKeyFormat = errors.New(`invalid key format: it should be"der" or "pem"`)
 
 func NewSigner(key *rsa.PrivateKey) *Signer {
 	return &Signer{Key: key}
@@ -19,23 +22,38 @@ type Signer struct {
 	Key *rsa.PrivateKey
 }
 
-func (s *Signer) SignTextures(ctx context.Context, textures string) (string, error) {
-	message := []byte(textures)
+func (s *Signer) Sign(data io.Reader) ([]byte, error) {
 	messageHash := sha1.New()
-	_, err := messageHash.Write(message)
+	_, err := io.Copy(messageHash, data)
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
 	messageHashSum := messageHash.Sum(nil)
 	signature, err := rsa.SignPKCS1v15(randomReader, s.Key, crypto.SHA1, messageHashSum)
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
-	return base64.StdEncoding.EncodeToString(signature), nil
+	return signature, nil
 }
 
-func (s *Signer) GetPublicKey(ctx context.Context) (*rsa.PublicKey, error) {
-	return &s.Key.PublicKey, nil
+func (s *Signer) GetPublicKey(format string) ([]byte, error) {
+	if format != "der" && format != "pem" {
+		return nil, invalidKeyFormat
+	}
+
+	asn1Bytes, err := x509.MarshalPKIXPublicKey(s.Key.Public())
+	if err != nil {
+		return nil, err
+	}
+
+	if format == "pem" {
+		return pem.EncodeToMemory(&pem.Block{
+			Type:  "PUBLIC KEY",
+			Bytes: asn1Bytes,
+		}), nil
+	}
+
+	return asn1Bytes, nil
 }