generator_rs256.go

// Copyright © 2017 Aeneas Rekkas <aeneas+oss@aeneas.io>
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package jwk

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"fmt"

	"github.com/pkg/errors"
	"github.com/square/go-jose"
)

type RS256Generator struct {
	KeyLength int
}

func (g *RS256Generator) Generate(id string) (*jose.JSONWebKeySet, error) {
	if g.KeyLength < 4096 {
		g.KeyLength = 4096
	}

	key, err := rsa.GenerateKey(rand.Reader, g.KeyLength)
	if err != nil {
		return nil, errors.Errorf("Could not generate key because %s", err)
	} else if err = key.Validate(); err != nil {
		return nil, errors.Errorf("Validation failed because %s", err)
	}

	// jose does not support this...
	key.Precomputed = rsa.PrecomputedValues{}
	return &jose.JSONWebKeySet{
		Keys: []jose.JSONWebKey{
			{
				Algorithm:    "RS256",
				Key:          key,
				KeyID:        ider("private", id),
				Certificates: []*x509.Certificate{},
			},
			{
				Algorithm:    "RS256",
				Key:          &key.PublicKey,
				KeyID:        ider("public", id),
				Certificates: []*x509.Certificate{},
			},
		},
	}, nil
}

func ider(typ, id string) string {
	if id != "" {
		return fmt.Sprintf("%s:%s", typ, id)
	}
	return typ
}