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// Copyright 2024 OpenPubkey
//
// 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.
//
// SPDX-License-Identifier: Apache-2.0
package cosigner
import (
"context"
"fmt"
"time"
"github.com/lestrrat-go/jwx/v2/jwa"
"github.com/lestrrat-go/jwx/v2/jws"
"github.com/openpubkey/openpubkey/discover"
"github.com/openpubkey/openpubkey/pktoken"
)
type DefaultCosignerVerifier struct {
issuer string
options CosignerVerifierOpts
}
type CosignerVerifierOpts struct {
// Strict specifies whether or not a pk token MUST contain a signature by this cosigner.
// Defaults to true.
Strict *bool
// Allows users to set custom function for discovering public key of Cosigner
DiscoverPublicKey *discover.PublicKeyFinder
}
func NewCosignerVerifier(issuer string, options CosignerVerifierOpts) *DefaultCosignerVerifier {
v := &DefaultCosignerVerifier{
issuer: issuer,
options: options,
}
// If no custom DiscoverPublicKey function is set, set default
if v.options.DiscoverPublicKey == nil {
v.options.DiscoverPublicKey = discover.DefaultPubkeyFinder()
}
// If strict is not set, then default it to true
if v.options.Strict == nil {
v.options.Strict = new(bool)
*v.options.Strict = true
}
return v
}
func (v *DefaultCosignerVerifier) Issuer() string {
return v.issuer
}
func (v *DefaultCosignerVerifier) Strict() bool {
return *v.options.Strict
}
func (v *DefaultCosignerVerifier) VerifyCosigner(ctx context.Context, pkt *pktoken.PKToken) error {
if pkt.Cos == nil {
return fmt.Errorf("no cosigner signature")
}
// Parse our header
header, err := pkt.ParseCosignerClaims()
if err != nil {
return err
}
if v.issuer != header.Issuer {
return fmt.Errorf("cosigner issuer (%s) doesn't match expected issuer (%s)", header.Issuer, v.issuer)
}
keyRecord, err := v.options.DiscoverPublicKey.ByKeyID(ctx, v.issuer, header.KeyID)
if err != nil {
return err
}
key := keyRecord.PublicKey
alg := keyRecord.Alg
// Check if it's expired
if time.Now().After(time.Unix(header.Expiration, 0)) {
return fmt.Errorf("cosigner signature expired")
}
if header.Algorithm != alg {
return fmt.Errorf("key (kid=%s) has alg (%s) which doesn't match alg (%s) in protected", header.KeyID, alg, header.Algorithm)
}
jwsPubkey := jws.WithKey(jwa.KeyAlgorithmFrom(alg), key)
_, err = jws.Verify(pkt.CosToken, jwsPubkey)
return err
}
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