Read or create private key using filepath

signer.go

@@ -2,7 +2,10 @@ package mjwt
 
 import (
 	"crypto/rsa"
+	"crypto/x509"
 	"github.com/golang-jwt/jwt/v4"
+	"io"
+	"os"
 	"time"
 )
 
@@ -25,6 +28,31 @@ func NewMJwtSigner(issuer string, key *rsa.PrivateKey) Signer {
 	}
 }
 
+// NewMJwtSignerFromFileOrCreate creates a new defaultMJwtSigner using the path
+// of a rsa.PrivateKey file. If the file does not exist then the file is created
+// and a new private key is generated.
+func NewMJwtSignerFromFileOrCreate(issuer, file string, random io.Reader, bits int) (Signer, error) {
+	privateKey, err := readOrCreatePrivateKey(file, random, bits)
+	if err != nil {
+		return nil, err
+	}
+	return NewMJwtSigner(issuer, privateKey), nil
+}
+
+// NewMJwtSignerFromFile creates a new defaultMJwtSigner using the path of a
+// rsa.PrivateKey file.
+func NewMJwtSignerFromFile(issuer, file string) (Signer, error) {
+	raw, err := os.ReadFile(file)
+	if err != nil {
+		return nil, err
+	}
+	key, err := x509.ParsePKCS1PrivateKey(raw)
+	if err != nil {
+		return nil, err
+	}
+	return NewMJwtSigner(issuer, key), nil
+}
+
 // Issuer returns the name of the issuer
 func (d *defaultMJwtSigner) Issuer() string { return d.issuer }
 
@@ -44,3 +72,41 @@ func (d *defaultMJwtSigner) SignJwt(wrapped jwt.Claims) (string, error) {
 func (d *defaultMJwtSigner) VerifyJwt(token string, claims baseTypeClaim) (*jwt.Token, error) {
 	return d.verify.VerifyJwt(token, claims)
 }
+
+// readOrCreatePrivateKey returns the private key it the file already exists,
+// generates a new private key and saves it to the file, or returns an error if
+// reading or generating failed.
+func readOrCreatePrivateKey(file string, random io.Reader, bits int) (*rsa.PrivateKey, error) {
+	// read the file or return nil
+	f, err := readOrEmptyFile(file)
+	if err != nil {
+		return nil, err
+	}
+	if f == nil {
+		// generate a new key
+		key, err := rsa.GenerateKey(random, bits)
+		if err != nil {
+			return nil, err
+		}
+
+		// write the key to the file
+		err = os.WriteFile(file, x509.MarshalPKCS1PrivateKey(key), 0600)
+		return key, err
+	} else {
+		// try to parse the private key
+		return x509.ParsePKCS1PrivateKey(f)
+	}
+}
+
+// readOrEmptyFile returns bytes and errors from os.ReadFile or (nil, nil) if the
+// file does not exist.
+func readOrEmptyFile(file string) ([]byte, error) {
+	raw, err := os.ReadFile(file)
+	if err == nil {
+		return raw, nil
+	}
+	if os.IsNotExist(err) {
+		return nil, nil
+	}
+	return nil, err
+}

signer_test.go

@@ -0,0 +1,62 @@
+package mjwt
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"github.com/stretchr/testify/assert"
+	"os"
+	"testing"
+)
+
+func TestNewMJwtSigner(t *testing.T) {
+	key, err := rsa.GenerateKey(rand.Reader, 2048)
+	assert.NoError(t, err)
+	NewMJwtSigner("Test", key)
+}
+
+func TestNewMJwtSignerFromFile(t *testing.T) {
+	tempKey, err := os.CreateTemp("", "key-test-*.pem")
+	assert.NoError(t, err)
+	key, err := rsa.GenerateKey(rand.Reader, 2048)
+	assert.NoError(t, err)
+	_, err = tempKey.Write(x509.MarshalPKCS1PrivateKey(key))
+	assert.NoError(t, err)
+	assert.NoError(t, tempKey.Close())
+	signer, err := NewMJwtSignerFromFile("Test", tempKey.Name())
+	assert.NoError(t, err)
+	assert.NoError(t, os.Remove(tempKey.Name()))
+	_, err = NewMJwtSignerFromFile("Test", tempKey.Name())
+	assert.Error(t, err)
+	assert.True(t, os.IsNotExist(err))
+	assert.True(t, signer.(*defaultMJwtSigner).key.Equal(key))
+}
+
+func TestNewMJwtSignerFromFileOrCreate(t *testing.T) {
+	tempKey, err := os.CreateTemp("", "key-test-*.pem")
+	assert.NoError(t, err)
+	assert.NoError(t, tempKey.Close())
+	assert.NoError(t, os.Remove(tempKey.Name()))
+	signer, err := NewMJwtSignerFromFileOrCreate("Test", tempKey.Name(), rand.Reader, 2048)
+	assert.NoError(t, err)
+	signer2, err := NewMJwtSignerFromFileOrCreate("Test", tempKey.Name(), rand.Reader, 2048)
+	assert.NoError(t, err)
+	assert.True(t, signer.(*defaultMJwtSigner).key.Equal(signer2.(*defaultMJwtSigner).key))
+}
+
+func TestReadOrCreatePrivateKey(t *testing.T) {
+	tempKey, err := os.CreateTemp("", "key-test-*.pem")
+	assert.NoError(t, err)
+	key, err := rsa.GenerateKey(rand.Reader, 2048)
+	assert.NoError(t, err)
+	_, err = tempKey.Write(x509.MarshalPKCS1PrivateKey(key))
+	assert.NoError(t, err)
+	assert.NoError(t, tempKey.Close())
+	key2, err := readOrCreatePrivateKey(tempKey.Name(), rand.Reader, 2048)
+	assert.NoError(t, err)
+	assert.True(t, key.Equal(key2))
+	assert.NoError(t, os.Remove(tempKey.Name()))
+	key3, err := readOrCreatePrivateKey(tempKey.Name(), rand.Reader, 2048)
+	assert.NoError(t, err)
+	assert.NoError(t, key3.Validate())
+}