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jwt.go
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jwt.go
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// Copyright 2021 The Witness Contributors
//
// 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 (
"encoding/json"
"fmt"
"net/http"
"github.com/in-toto/go-witness/attestation"
"github.com/invopop/jsonschema"
"gopkg.in/square/go-jose.v2"
"gopkg.in/square/go-jose.v2/jwt"
)
const (
Name = "jwt"
Type = "https://witness.dev/attestations/jwt/v0.1"
RunType = attestation.PreMaterialRunType
)
// This is a hacky way to create a compile time error in case the attestor
// doesn't implement the expected interfaces.
var (
_ attestation.Attestor = &Attestor{}
)
func init() {
attestation.RegisterAttestation(Name, Type, RunType, func() attestation.Attestor {
return New()
})
}
type ErrInvalidToken string
func (e ErrInvalidToken) Error() string {
return fmt.Sprintf("invalid token: \"%v\"", string(e))
}
type Option func(a *Attestor)
type VerificationInfo struct {
JWKSUrl string `json:"jwksUrl"`
JWK jose.JSONWebKey `json:"jwk"`
}
type Attestor struct {
Claims map[string]interface{} `json:"claims"`
VerifiedBy VerificationInfo `json:"verifiedBy,omitempty"`
jwksUrl string
token string
}
func WithToken(token string) Option {
return func(a *Attestor) {
a.token = token
}
}
func WithJWKSUrl(url string) Option {
return func(a *Attestor) {
a.jwksUrl = url
}
}
func New(opts ...Option) *Attestor {
a := &Attestor{
Claims: make(map[string]interface{}),
}
for _, opt := range opts {
opt(a)
}
return a
}
func (a *Attestor) Schema() *jsonschema.Schema {
return jsonschema.Reflect(&a)
}
func (a *Attestor) Attest(ctx *attestation.AttestationContext) error {
if a.token == "" {
return ErrInvalidToken(a.token)
}
parsed, err := jwt.ParseSigned(a.token)
if err != nil {
return fmt.Errorf("error parsing token: %w", err)
}
resp, err := http.Get(a.jwksUrl)
if err != nil {
return fmt.Errorf("error fetching jwks: %w", err)
}
defer resp.Body.Close()
jwks := jose.JSONWebKeySet{}
decoder := json.NewDecoder(resp.Body)
if err := decoder.Decode(&jwks); err != nil {
return fmt.Errorf("error decoding jwks: %w", err)
}
if err := parsed.Claims(jwks, &a.Claims); err != nil {
return fmt.Errorf("error parsing claims: %w", err)
}
keyID := ""
for _, header := range parsed.Headers {
if header.KeyID != "" {
keyID = header.KeyID
break
}
}
possibleJwk := jwks.Key(keyID)
if len(possibleJwk) <= 0 {
return nil
}
a.VerifiedBy = VerificationInfo{
JWKSUrl: a.jwksUrl,
JWK: possibleJwk[0],
}
return nil
}
func (a *Attestor) Name() string {
return Name
}
func (a *Attestor) Type() string {
return Type
}
func (a *Attestor) RunType() attestation.RunType {
return RunType
}