Add Chef package registry (#22554)

This PR implements a [Chef registry](https://chef.io/) to manage
cookbooks. This package type was a bit complicated because Chef uses RSA
signed requests as authentication with the registry.


![grafik](https://user-images.githubusercontent.com/1666336/213747995-46819fd8-c3d6-45a2-afd4-a4c3c8505a4a.png)


![grafik](https://user-images.githubusercontent.com/1666336/213748145-d01c9e81-d4dd-41e3-a3cc-8241862c3166.png)

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/util/keypair_test.go

@@ -0,0 +1,61 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package util
+
+import (
+	"crypto"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	"encoding/pem"
+	"regexp"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestKeygen(t *testing.T) {
+	priv, pub, err := GenerateKeyPair(2048)
+	assert.NoError(t, err)
+
+	assert.NotEmpty(t, priv)
+	assert.NotEmpty(t, pub)
+
+	assert.Regexp(t, regexp.MustCompile("^-----BEGIN RSA PRIVATE KEY-----.*"), priv)
+	assert.Regexp(t, regexp.MustCompile("^-----BEGIN PUBLIC KEY-----.*"), pub)
+}
+
+func TestSignUsingKeys(t *testing.T) {
+	priv, pub, err := GenerateKeyPair(2048)
+	assert.NoError(t, err)
+
+	privPem, _ := pem.Decode([]byte(priv))
+	if privPem == nil || privPem.Type != "RSA PRIVATE KEY" {
+		t.Fatal("key is wrong type")
+	}
+
+	privParsed, err := x509.ParsePKCS1PrivateKey(privPem.Bytes)
+	assert.NoError(t, err)
+
+	pubPem, _ := pem.Decode([]byte(pub))
+	if pubPem == nil || pubPem.Type != "PUBLIC KEY" {
+		t.Fatal("key failed to decode")
+	}
+
+	pubParsed, err := x509.ParsePKIXPublicKey(pubPem.Bytes)
+	assert.NoError(t, err)
+
+	// Sign
+	msg := "activity pub is great!"
+	h := sha256.New()
+	h.Write([]byte(msg))
+	d := h.Sum(nil)
+	sig, err := rsa.SignPKCS1v15(rand.Reader, privParsed, crypto.SHA256, d)
+	assert.NoError(t, err)
+
+	// Verify
+	err = rsa.VerifyPKCS1v15(pubParsed.(*rsa.PublicKey), crypto.SHA256, d, sig)
+	assert.NoError(t, err)
+}