update for using reflect instead of mapstructure

Signed-off-by: Javan lacerda <javanlacerda@google.com>

go.mod

@@ -22,7 +22,6 @@ require (
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.20.0
 	github.com/hashicorp/golang-lru v1.0.2
 	github.com/magiconair/properties v1.8.7
-	github.com/mitchellh/mapstructure v1.5.0
 	github.com/prometheus/client_golang v1.19.1
 	github.com/prometheus/client_model v0.6.1
 	github.com/prometheus/common v0.54.0
@@ -111,6 +110,7 @@ require (
 	github.com/letsencrypt/boulder v0.0.0-20230907030200-6d76a0f91e1e // indirect
 	github.com/miekg/pkcs11 v1.1.1 // indirect
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
+	github.com/mitchellh/mapstructure v1.5.0 // indirect
 	github.com/opencontainers/go-digest v1.0.0 // indirect
 	github.com/pelletier/go-toml/v2 v2.2.2 // indirect
 	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect

pkg/config/config.go

@@ -32,7 +32,6 @@ import (
 
 	"github.com/coreos/go-oidc/v3/oidc"
 	lru "github.com/hashicorp/golang-lru"
-	"github.com/mitchellh/mapstructure"
 	"github.com/sigstore/fulcio/pkg/certificate"
 	fulciogrpc "github.com/sigstore/fulcio/pkg/generated/protobuf"
 	"github.com/sigstore/fulcio/pkg/log"
@@ -470,18 +469,16 @@ func validateCIIssuerMetadata(fulcioConfig *FulcioConfig) error {
 	}
 
 	for _, ciIssuerMetadata := range fulcioConfig.CIIssuerMetadata {
-		claimsTemplates := make(map[string]interface{})
-		err := mapstructure.Decode(ciIssuerMetadata.ExtensionTemplates, &claimsTemplates)
-		if err != nil {
-			return err
-		}
-		for _, temp := range claimsTemplates {
-			err := checkParse(temp)
+		v := reflect.Indirect(reflect.ValueOf(&ciIssuerMetadata.ExtensionTemplates))
+		for i := 0; i < v.NumField(); i++ {
+			s := v.Field(i).String()
+			err := checkParse(s)
 			if err != nil {
 				return err
 			}
 		}
-		err = checkParse(ciIssuerMetadata.SubjectAlternativeNameTemplate)
+
+		err := checkParse(ciIssuerMetadata.SubjectAlternativeNameTemplate)
 		if err != nil {
 			return err
 		}

pkg/identity/ciprovider/principal.go

@@ -21,11 +21,10 @@ import (
 	"fmt"
 	"html/template"
 	"net/url"
+	"reflect"
 	"strings"
 
 	"github.com/coreos/go-oidc/v3/oidc"
-	"github.com/mitchellh/mapstructure"
-	"github.com/sigstore/fulcio/pkg/certificate"
 	"github.com/sigstore/fulcio/pkg/config"
 	"github.com/sigstore/fulcio/pkg/identity"
 )
@@ -127,33 +126,24 @@ func (principal ciPrincipal) Embed(_ context.Context, cert *x509.Certificate) er
 	}
 	uris := []*url.URL{sanURL}
 	cert.URIs = uris
-	mapExtensionsForTemplate := make(map[string]interface{})
-	err = mapstructure.Decode(claimsTemplates, &mapExtensionsForTemplate)
-	if err != nil {
-		return err
-	}
-
-	for k, v := range mapValuesToString(mapExtensionsForTemplate) {
-		// It avoids to try applying template or replace for a empty string.
-		if v != "" {
-			mapExtensionsForTemplate[k], err = applyTemplateOrReplace(v, claims, defaults)
-			if err != nil {
-				return err
-			}
+	v := reflect.Indirect(reflect.ValueOf(&claimsTemplates))
+	for i := 0; i < v.NumField(); i++ {
+		s := v.Field(i).String() // value of each field, e.g the template string
+		if s == "" {
+			continue
 		}
+		extValue, err := applyTemplateOrReplace(s, claims, defaults)
+		if err != nil {
+			return err
+		}
+		v.Field(i).SetString(extValue)
 	}
-	ext := &certificate.Extensions{
-		Issuer: principal.Token.Issuer,
-	}
-	err = mapstructure.Decode(mapExtensionsForTemplate, &ext)
-	if err != nil {
-		return err
-	}
+
 	// Guarantees to set the extension issuer as the token issuer
 	// regardless of whether this field has been set before
-	ext.Issuer = principal.Token.Issuer
+	claimsTemplates.Issuer = principal.Token.Issuer
 	// Embed additional information into custom extensions
-	cert.ExtraExtensions, err = ext.Render()
+	cert.ExtraExtensions, err = claimsTemplates.Render()
 	if err != nil {
 		return err
 	}