examples: This adds example code on how to fetch a fulcio certificate

examples/README.md

@@ -0,0 +1,10 @@
+fulcio examples
+===============
+
+This directory contains example code that shows how one utilize the fulcio
+library for certificate generation.
+
+# request-certificate
+This code is a minimal example how one would request a short-lived certificate
+(20 minutes) for code signing. It uses the fulcio oauth portal and generates a
+RSA 4096 key.

examples/request-certificate/main.go

@@ -0,0 +1,99 @@
+// Copyright 2022 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 main
+
+import (
+	"bytes"
+	"crypto"
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+	"log"
+	"net/url"
+
+	"github.com/sigstore/fulcio/pkg/api"
+	"github.com/sigstore/sigstore/pkg/oauthflow"
+	"github.com/sigstore/sigstore/pkg/signature"
+	"github.com/sigstore/sigstore/pkg/signature/options"
+)
+
+var (
+	fulcioUrl    = "https://fulcio.sigstore.dev"
+	oidcIssuer   = "https://oauth2.sigstore.dev/auth"
+	oidcClientID = "sigstore"
+)
+
+// Some of this is just ripped from cosign
+func GetCert(signer *signature.RSAPKCS1v15SignerVerifier, fc api.Client, oidcIssuer string, oidcClientID string) (*api.CertificateResponse, error) {
+
+	tok, err := oauthflow.OIDConnect(oidcIssuer, oidcClientID, "", "", oauthflow.DefaultIDTokenGetter)
+	if err != nil {
+		return nil, err
+	}
+
+	// Sign the email address as part of the request
+	b := bytes.NewBuffer([]byte(tok.Subject))
+	proof, err := signer.SignMessage(b, options.WithCryptoSignerOpts(crypto.SHA256))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	pubBytes, err := x509.MarshalPKIXPublicKey(signer.Public())
+	if err != nil {
+		return nil, err
+	}
+	cr := api.CertificateRequest{
+		PublicKey: api.Key{
+			Algorithm: "rsa4096",
+			Content:   pubBytes,
+		},
+		SignedEmailAddress: proof,
+	}
+	return fc.SigningCert(cr, tok.RawString)
+}
+
+func NewClient(fulcioURL string) (api.Client, error) {
+	fulcioServer, err := url.Parse(fulcioURL)
+	if err != nil {
+		return nil, err
+	}
+	fClient := api.NewClient(fulcioServer, api.WithUserAgent("Fulcio Example Code"))
+	return fClient, nil
+}
+
+func main() {
+	signer, _, err := signature.NewDefaultRSAPKCS1v15SignerVerifier()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fClient, err := NewClient(fulcioUrl)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	certResp, err := GetCert(signer, fClient, oidcIssuer, oidcClientID)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	clientPEM, _ := pem.Decode([]byte(certResp.CertPEM))
+	cert, err := x509.ParseCertificate(clientPEM.Bytes)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Println("Received signing cerificate with serial number: ", cert.SerialNumber)
+}

go.sum

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