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// Copyright 2024 The Sigstore Authors.
//
// 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 ciprovider
import (
"bytes"
"context"
"crypto/x509"
"encoding/json"
"fmt"
"html/template"
"net/url"
"reflect"
"strings"
"github.com/coreos/go-oidc/v3/oidc"
"github.com/sigstore/fulcio/pkg/config"
"github.com/sigstore/fulcio/pkg/identity"
)
func mapValuesToString(claims map[string]interface{}) map[string]string {
newMap := make(map[string]string)
for k, v := range claims {
newMap[k] = fmt.Sprintf("%s", v)
}
return newMap
}
func getTokenClaims(token *oidc.IDToken) (map[string]string, error) {
var tokenClaims map[string]interface{}
if err := token.Claims(&tokenClaims); err != nil {
return nil, err
}
return mapValuesToString(tokenClaims), nil
}
// It makes string interpolation for a given string by using the
// templates syntax https://pkg.go.dev/text/template
// logMetadata added as a parameter for having a richer log
func applyTemplateOrReplace(
extValueTemplate string, tokenClaims map[string]string,
issuerMetadata map[string]string, logMetadata map[string]string) (string, error) {
// Here we merge the data from was claimed by the id token with the
// default data provided by the yaml file.
// The order here matter because we want to override the claimed data
// with the default data.
// The claimed data will have priority over the default data.
mergedData := make(map[string]string)
for k, v := range issuerMetadata {
mergedData[k] = v
}
for k, v := range tokenClaims {
mergedData[k] = v
}
if strings.Contains(extValueTemplate, "{{") {
var doc bytes.Buffer
// This option forces to having the claim that is required
// for the template
t := template.New("").Option("missingkey=error")
// It shouldn't raise error since we already checked all
// templates in validateCIIssuerMetadata functions in config.go
p, err := t.Parse(extValueTemplate)
if err != nil {
return "", err
}
err = p.Execute(&doc, mergedData)
if err != nil {
return "", err
}
return doc.String(), nil
}
claimValue, ok := mergedData[extValueTemplate]
if !ok {
var jsonMetadata bytes.Buffer
inrec, _ := json.Marshal(logMetadata)
_ = json.Indent(&jsonMetadata, inrec, "", "\t")
return "", fmt.Errorf("value <%s> not present in either claims or defaults. %s", extValueTemplate, jsonMetadata.String())
}
return claimValue, nil
}
type ciPrincipal struct {
Token *oidc.IDToken
ClaimsMetadata config.IssuerMetadata
}
func WorkflowPrincipalFromIDToken(ctx context.Context, token *oidc.IDToken) (identity.Principal, error) {
cfg := config.FromContext(ctx)
issuerCfg, ok := cfg.GetIssuer(token.Issuer)
if !ok {
return nil, fmt.Errorf("configuration can not be loaded for issuer %v", token.Issuer)
}
metadata, ok := cfg.CIIssuerMetadata[issuerCfg.CIProvider]
if !ok {
return nil, fmt.Errorf(
"metadata not found for ci provider %s, issuer: %s", issuerCfg.CIProvider, token.Issuer)
}
return ciPrincipal{
token,
metadata,
}, nil
}
func (principal ciPrincipal) Name(_ context.Context) string {
return principal.Token.Subject
}
func (principal ciPrincipal) Embed(_ context.Context, cert *x509.Certificate) error {
claimsTemplates := principal.ClaimsMetadata.ExtensionTemplates
defaults := principal.ClaimsMetadata.DefaultTemplateValues
claims, err := getTokenClaims(principal.Token)
if err != nil {
return err
}
if strings.TrimSpace(principal.ClaimsMetadata.SubjectAlternativeNameTemplate) == "" {
return fmt.Errorf("SubjectAlternativeNameTemplate should not be empty. Issuer: %s", principal.Token.Issuer)
}
subjectAlternativeName, err := applyTemplateOrReplace(
principal.ClaimsMetadata.SubjectAlternativeNameTemplate, claims, defaults,
map[string]string{
"Issuer": principal.Token.Issuer,
"ExtensionName": "SubjectAlternativeName",
})
if err != nil {
return err
}
sanURL, err := url.Parse(subjectAlternativeName)
if err != nil {
return err
}
uris := []*url.URL{sanURL}
cert.URIs = uris
// We should use value.Elem() here as we need a
// addressable reference of the templates for applying the SetString().
v := reflect.ValueOf(&claimsTemplates).Elem()
// Type of the reflect value is needed as it is necessary
// for getting the field name.
vType := v.Type()
for i := 0; i < v.NumField(); i++ {
s := v.Field(i).String() // value of each field, e.g the template string
// We check the field name to avoid to apply the template for the Issuer
// Issuer field should always come from the token issuer
if strings.TrimSpace(s) == "" || vType.Field(i).Name == "Issuer" {
continue
}
extValue, err := applyTemplateOrReplace(s, claims, defaults,
map[string]string{
"Issuer": principal.Token.Issuer,
"ExtensionName": vType.Field(i).Name,
})
if err != nil {
return err
}
v.Field(i).SetString(extValue)
}
// Guarantees to set the extension issuer as the token issuer
// regardless of whether this field has been set before
claimsTemplates.Issuer = principal.Token.Issuer
// Embed additional information into custom extensions
cert.ExtraExtensions, err = claimsTemplates.Render()
if err != nil {
return err
}
return nil
}
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