如何在 Go 中创建使用 TLS 客户端身份验证的测试服务器？

Question

我想为从设备证书中提取某些信息的 HTTP 处理程序编写单元测试。我找到了这个要点 https://gist.github.com/ncw/9253562，它使用 openssl 生成证书并简单地读取其 client.go 和 server.go 中的结果文件。但是，为了使事情更加透明，我想使用 Go 的标准库生成证书。

这是我迄今为止在单元测试中的尝试（可在 https://github.com/kurtpeek/client-auth-test 获得）：

package main

import (
    "crypto"
    "crypto/rand"
    "crypto/rsa"
    "crypto/sha1"
    "crypto/tls"
    "crypto/x509"
    "crypto/x509/pkix"
    "encoding/asn1"
    "encoding/pem"
    "io"
    "math/big"
    "net"
    "net/http"
    "net/http/httptest"
    "testing"
    "time"

    "github.com/stretchr/testify/assert"
    "github.com/stretchr/testify/require"
)

func TestDeviceFromTLS(t *testing.T) {
    deviceKeyPEM, csrPEM := generateKeyAndCSR(t)

    caKey, caKeyPEM := generateKey(t)
    caCert, caCertPEM := generateRootCert(t, caKey)

    deviceCertPEM := signCSR(t, csrPEM, caKey, caCert)

    serverCert, err := tls.X509KeyPair(caCertPEM, caKeyPEM)
    require.NoError(t, err)

    clientPool := x509.NewCertPool()
    clientPool.AddCert(caCert)

    ts := httptest.NewUnstartedServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        assert.Len(t, r.TLS.PeerCertificates, 1)
    }))
    ts.TLS = &tls.Config{
        Certificates: []tls.Certificate{serverCert},
        ClientAuth:   tls.RequireAndVerifyClientCert,
        ClientCAs:    clientPool,
    }
    ts.StartTLS()
    defer ts.Close()

    deviceCert, err := tls.X509KeyPair(deviceCertPEM, deviceKeyPEM)
    require.NoError(t, err)

    pool := x509.NewCertPool()
    pool.AddCert(caCert)

    client := ts.Client()
    client.Transport.(*http.Transport).TLSClientConfig = &tls.Config{
        Certificates: []tls.Certificate{deviceCert},
        RootCAs:      pool,
    }

    req, err := http.NewRequest(http.MethodPut, ts.URL, nil)
    resp, err := client.Do(req)
    require.NoError(t, err)
    defer resp.Body.Close()

    assert.Exactly(t, http.StatusOK, resp.StatusCode)
}

func generateKeyAndCSR(t *testing.T) ([]byte, []byte) {
    rsaKey, err := rsa.GenerateKey(rand.Reader, 1024)
    require.NoError(t, err)

    key := pem.EncodeToMemory(&pem.Block{
        Type:  "RSA PRIVATE KEY",
        Bytes: x509.MarshalPKCS1PrivateKey(rsaKey),
    })

    template := &x509.CertificateRequest{
        Subject: pkix.Name{
            Country:      []string{"US"},
            Locality:     []string{"San Francisco"},
            Organization: []string{"Awesomeness, Inc."},
            Province:     []string{"California"},
        },
        SignatureAlgorithm: x509.SHA256WithRSA,
        IPAddresses:        []net.IP{net.ParseIP("127.0.0.1")},
    }

    req, err := x509.CreateCertificateRequest(rand.Reader, template, rsaKey)
    require.NoError(t, err)

    csr := pem.EncodeToMemory(&pem.Block{
        Type:  "CERTIFICATE REQUEST",
        Bytes: req,
    })

    return key, csr
}

func generateRootCert(t *testing.T, key crypto.Signer) (*x509.Certificate, []byte) {
    subjectKeyIdentifier := calculateSubjectKeyIdentifier(t, key.Public())

    template := &x509.Certificate{
        SerialNumber: generateSerial(t),
        Subject: pkix.Name{
            Organization: []string{"Awesomeness, Inc."},
            Country:      []string{"US"},
            Locality:     []string{"San Francisco"},
        },
        NotBefore:             time.Now(),
        NotAfter:              time.Now().AddDate(10, 0, 0),
        SubjectKeyId:          subjectKeyIdentifier,
        AuthorityKeyId:        subjectKeyIdentifier,
        KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,
        ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth},
        BasicConstraintsValid: true,
        IsCA:                  true,
        MaxPathLenZero:        true,
    }

    der, err := x509.CreateCertificate(rand.Reader, template, template, key.Public(), key)
    require.NoError(t, err)

    rootCert, err := x509.ParseCertificate(der)
    require.NoError(t, err)

    rootCertPEM := pem.EncodeToMemory(&pem.Block{
        Type:  "CERTIFICATE",
        Bytes: der,
    })

    return rootCert, rootCertPEM
}

// generateSerial generates a serial number using the maximum number of octets (20) allowed by RFC 5280 4.1.2.2
// (Adapted from https://github.com/cloudflare/cfssl/blob/828c23c22cbca1f7632b9ba85174aaa26e745340/signer/local/local.go#L407-L418)
func generateSerial(t *testing.T) *big.Int {
    serialNumber := make([]byte, 20)
    _, err := io.ReadFull(rand.Reader, serialNumber)
    require.NoError(t, err)

    return new(big.Int).SetBytes(serialNumber)
}

// calculateSubjectKeyIdentifier implements a common method to generate a key identifier
// from a public key, namely, by composing it from the 160-bit SHA-1 hash of the bit string
// of the public key (cf. https://tools.ietf.org/html/rfc5280#section-4.2.1.2).
// (Adapted from https://github.com/jsha/minica/blob/master/main.go).
func calculateSubjectKeyIdentifier(t *testing.T, pubKey crypto.PublicKey) []byte {
    spkiASN1, err := x509.MarshalPKIXPublicKey(pubKey)
    require.NoError(t, err)

    var spki struct {
        Algorithm        pkix.AlgorithmIdentifier
        SubjectPublicKey asn1.BitString
    }
    _, err = asn1.Unmarshal(spkiASN1, &spki)
    require.NoError(t, err)

    skid := sha1.Sum(spki.SubjectPublicKey.Bytes)
    return skid[:]
}

// signCSR signs a certificate signing request with the given CA certificate and private key
func signCSR(t *testing.T, csr []byte, caKey crypto.Signer, caCert *x509.Certificate) []byte {
    block, _ := pem.Decode(csr)
    require.NotNil(t, block, "failed to decode CSR")

    certificateRequest, err := x509.ParseCertificateRequest(block.Bytes)
    require.NoError(t, err)

    require.NoError(t, certificateRequest.CheckSignature())

    template := x509.Certificate{
        Subject:               certificateRequest.Subject,
        PublicKeyAlgorithm:    certificateRequest.PublicKeyAlgorithm,
        PublicKey:             certificateRequest.PublicKey,
        SignatureAlgorithm:    certificateRequest.SignatureAlgorithm,
        Signature:             certificateRequest.Signature,
        SerialNumber:          generateSerial(t),
        Issuer:                caCert.Issuer,
        NotBefore:             time.Now(),
        NotAfter:              time.Now().AddDate(10, 0, 0),
        KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageKeyEncipherment,
        ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth},
        SubjectKeyId:          calculateSubjectKeyIdentifier(t, certificateRequest.PublicKey),
        BasicConstraintsValid: true,
        IPAddresses:           certificateRequest.IPAddresses,
    }

    derBytes, err := x509.CreateCertificate(rand.Reader, &template, caCert, certificateRequest.PublicKey, caKey)
    require.NoError(t, err)

    return pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
}

// generateKey generates a 1024-bit RSA private key
func generateKey(t *testing.T) (crypto.Signer, []byte) {
    key, err := rsa.GenerateKey(rand.Reader, 1024)
    require.NoError(t, err)

    keyPEM := pem.EncodeToMemory(&pem.Block{
        Type:  "RSA PRIVATE KEY",
        Bytes: x509.MarshalPKCS1PrivateKey(key),
    })

    return key, keyPEM
}

但是，当我运行它时，出现以下错误：

> go test ./...
2020/04/06 15:12:30 http: TLS handshake error from 127.0.0.1:58685: remote error: tls: bad certificate
--- FAIL: TestDeviceFromTLS (0.05s)
    main_test.go:64: 
            Error Trace:    main_test.go:64
            Error:          Received unexpected error:
                            Put https://127.0.0.1:58684: x509: cannot validate certificate for 127.0.0.1 because it doesn't contain any IP SANs
            Test:           TestDeviceFromTLS
FAIL
FAIL    github.com/kurtpeek/client-auth-test    0.379s

我不太确定错误消息的含义

cannot validate certificate for 127.0.0.1 because it doesn't contain any IP SANs

因为我在创建证书时传入了 IPAddresses 字段。对这里有什么问题有什么想法吗？

Answer 1

仔细观察 ncw 的要点，我注意到一个关键区别是客户端 TLS 配置中的 InsecureSkipVerify 选项设置为 true。我添加了这个，所以

    client.Transport.(*http.Transport).TLSClientConfig = &tls.Config{
        Certificates:       []tls.Certificate{deviceCert},
        RootCAs:            pool,
        InsecureSkipVerify: true,
    }

现在测试通过了。

服务器证书的验证超出了本次测试的范围，所以这足以满足我的目的，但我仍然想知道验证失败的原因。

Answer 2

该错误与 X509 证书中存在的 SAN 字段扩展有关。 X509 证书中的 SAN 字段可以包含以下类型的条目；

DNS 名称
IP 地址
URI

详情可见here

通常在证书验证过程中，可以在某些系统上执行 SAN 扩展验证。因此你看到这样的错误信息

您有两个选项可以避免此错误消息，

在您的证书中添加 SAN IP 字段
跳过证书验证步骤[这是您通过注释完成的步骤]

Answer 3

I'm not really sure what to make of the error message

cannot validate certificate for 127.0.0.1 because it doesn't contain any IP SANs

因为我在传递 IPAddresses 字段时创建证书。关于这里有什么问题有什么想法吗？

问题是您在创建 client 证书时传递了 IPAddresses 字段，但在创建 server 证书，因为你的服务器只是使用 CA 证书作为自己的证书，并且 CA 证书（正确地）不包含 IP 地址，因此错误消息是正确的：

caKey, caKeyPEM := generateKey(t)
caCert, caCertPEM := generateRootCert(t, caKey)

serverCert, err := tls.X509KeyPair(caCertPEM, caKeyPEM)

您应该创建由 CA（或 a CA）签署的服务器证书，与创建客户端证书的方式相同，并将其用于测试服务器。

一般来说，让一个密钥以您正在执行的方式执行作为 CA 和 TLS 服务器的双重职责是自找麻烦，在这里没有充分的理由这样做；虽然 RFC5280 实际上并没有禁止这种做法，但它至少似乎不鼓励这种做法，除非特殊情况需要。

尽管如此，您使用 CA 证书的方式在技术上不符合 RFC5280，因为它包含一个扩展的密钥使用扩展，仅指定 TLS 客户端和服务器身份验证，但您使用它来签署证书。它可能是宽容的，但在没有 anyExtendedKeyUsage 关键目的的情况下 x509.CreateCertificate 真的应该失败，在这里。

如何在 Go 中创建使用 TLS 客户端身份验证的测试服务器？

How to create a test server which uses TLS client authentication in Go?

go

ssl

x509

pem

ssl-client-authentication