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// Copyright 2025 Google LLC
//
// 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 jwt
import (
"fmt"
"github.com/tink-crypto/tink-go/v2/internal/internalapi"
"github.com/tink-crypto/tink-go/v2/jwt/jwthmac"
"github.com/tink-crypto/tink-go/v2/key"
"github.com/tink-crypto/tink-go/v2/mac/hmac"
)
type fullMac struct {
m *macWithKID
// kid is set only for TINK keys. Keys with Custom KID or that ignores
// it are RAW, thus this is nil.
kid *string
}
var _ MAC = (*fullMac)(nil)
func (s *fullMac) ComputeMACAndEncode(token *RawJWT) (string, error) {
return s.m.ComputeMACAndEncodeWithKID(token, s.kid)
}
func (s *fullMac) VerifyMACAndDecode(compact string, validator *Validator) (*VerifiedJWT, error) {
return s.m.VerifyMACAndDecodeWithKID(compact, validator, s.kid)
}
func createJWTHMAC(key key.Key) (any, error) {
jwthmacKey, ok := key.(*jwthmac.Key)
if !ok {
return nil, fmt.Errorf("createJWTHMAC: key is of type %T, want %T", key, (*jwthmac.Key)(nil))
}
jwtParams := jwthmacKey.Parameters().(*jwthmac.Parameters)
var hashType hmac.HashType
var tagSizeInBytes int
switch jwtParams.Algorithm() {
case jwthmac.HS256:
hashType = hmac.SHA256
tagSizeInBytes = 32
case jwthmac.HS384:
hashType = hmac.SHA384
tagSizeInBytes = 48
case jwthmac.HS512:
hashType = hmac.SHA512
tagSizeInBytes = 64
default:
return nil, fmt.Errorf("createJWTHMAC: unsupported algorithm: %s", jwtParams.Algorithm())
}
hmacParams, err := hmac.NewParameters(hmac.ParametersOpts{
KeySizeInBytes: jwtParams.KeySizeInBytes(),
TagSizeInBytes: tagSizeInBytes,
HashType: hashType,
Variant: hmac.VariantNoPrefix,
})
if err != nil {
return nil, fmt.Errorf("createJWTHMAC: %v", err)
}
hmacKey, err := hmac.NewKey(jwthmacKey.KeyBytes(), hmacParams, 0)
if err != nil {
return nil, fmt.Errorf("createJWTHMAC: %v", err)
}
mac, err := hmac.NewMAC(hmacKey, internalapi.Token{})
if err != nil {
return nil, fmt.Errorf("createJWTHMAC: %v", err)
}
var kid, customKID *string
kidValue, hasKID := jwthmacKey.KID()
switch jwtParams.KIDStrategy() {
case jwthmac.CustomKID:
if !hasKID {
// This should never happen.
return nil, fmt.Errorf("createJWTHMAC: CustomKID strategy requires a KID")
}
customKID = &kidValue
kid = nil
case jwthmac.Base64EncodedKeyIDAsKID:
if !hasKID {
// This should never happen.
return nil, fmt.Errorf("createJWTHMAC: Base64EncodedKeyIDAsKID strategy requires a KID")
}
kid = &kidValue
customKID = nil
case jwthmac.IgnoredKID:
kid = nil
customKID = nil
default:
// This should never happen.
return nil, fmt.Errorf("createJWTHMAC: unsupported KID strategy: %s", jwtParams.KIDStrategy())
}
macWithKID, err := newMACWithKID(mac, jwtParams.Algorithm().String(), customKID)
if err != nil {
return nil, fmt.Errorf("createJWTHMAC: %v", err)
}
return &fullMac{m: macWithKID, kid: kid}, nil
}
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