主代码:
package rsa

import (
    "crypto/rand"
    "crypto/rsa"
    "crypto/x509"
    "crypto/x509/pkix"
    "encoding/pem"
    "io/IoUtil"
    "math/big"
    rd "math/rand"
    "os"
    "time"
)

func init() {
    rd.Seed(time.Now().UnixNano())
}

type CertInformation struct {
    Country            []string
    Organization       []string
    OrganizationalUnit []string
    EmailAddress       []string
    Province           []string
    Locality           []string
    CommonName         string
    CrtName,KeyName   string
    IsCA               bool
    Names              []pkix.AttributeTypeAndValue
}

func CreateCRT(RootCa *x509.Certificate,RootKey *rsa.PrivateKey,info CertInformation) error {
    Crt := newCertificate(info)
    Key,err := rsa.GenerateKey(rand.Reader, 2048)
    if err != nil {
        return err
    }

    var buf []byte
    if RootCa == nil || RootKey == nil {
        //创建自签名证书
        buf,err = x509.CreateCertificate(rand.Reader,Crt,&Key.PublicKey,Key)
    } else {
        //使用根证书签名
        buf,RootCa,RootKey)
    }
    if err != nil {
        return err
    }

    err = write(info.CrtName,"CERTIFICATE",buf)
    if err != nil {
        return err
    }

    buf = x509.MarshalPKCS1PrivateKey(Key)
    return write(info.KeyName,"PRIVATE KEY",buf)
}
//编码写入文件
func write(filename,Type string,p []byte) error {
    File,err := os.Create(filename)
    defer File.Close()
    if err != nil {
        return err
    }
    var b *pem.Block = &pem.Block{Bytes: p,Type: Type}
    return pem.Encode(File,b)
}

func Parse(crtPath,keyPath string) (rootcertificate *x509.Certificate,rootPrivateKey *rsa.PrivateKey,err error) {
    rootcertificate,err = ParseCrt(crtPath)
    if err != nil {
        return
    }
    rootPrivateKey,err = ParseKey(keyPath)
    return
}

func ParseCrt(path string) (*x509.Certificate,error) {
    buf,err := IoUtil.ReadFile(path)
    if err != nil {
        return nil,err
    }
    p := &pem.Block{}
    p,buf = pem.Decode(buf)
    return x509.ParseCertificate(p.Bytes)
}

func ParseKey(path string) (*rsa.PrivateKey,err
    }
    p,buf := pem.Decode(buf)
    return x509.ParsePKCS1PrivateKey(p.Bytes)
}

func newCertificate(info CertInformation) *x509.Certificate {
    return &x509.Certificate{
        SerialNumber: big.NewInt(rd.Int63()),Subject: pkix.Name{
            Country:            info.Country,Organization:       info.Organization,OrganizationalUnit: info.OrganizationalUnit,Province:           info.Province,CommonName:         info.CommonName,Locality:           info.Locality,ExtraNames:         info.Names,},NotBefore:             time.Now(),//证书的开始时间
        NotAfter:              time.Now().AddDate(20, 0, 0),//证书的结束时间
        BasicConstraintsValid: true,//基本的有效性约束
        IsCA:           info.IsCA,//是否是根证书
        ExtKeyUsage:    []x509.ExtKeyUsage{x509.ExtKeyUsageClientAuth,x509.ExtKeyUsageServerAuth},//证书用途
        KeyUsage:       x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign,EmailAddresses: info.EmailAddress,}
}

测试代码:
package rsa

import (
    "crypto/x509/pkix"
    "encoding/asn1"
    "os"
    "testing"
)

func Test_crt(t *testing.T) {
    baseinfo := CertInformation{Country: []string{"CN"},Organization: []string{"WS"},IsCA: true,OrganizationalUnit: []string{"work-stacks"},EmailAddress: []string{"czxichen@163.com"},Locality: []string{"SuZhou"},Province: []string{"JiangSu"},CommonName: "Work-Stacks",CrtName: "test_root.crt",KeyName: "test_root.key"}

    err := CreateCRT(nil,nil,baseinfo)
    if err != nil {
        t.Log("Create crt error,Error info:",err)
        return
    }
    crtinfo := baseinfo
    crtinfo.IsCA = false
    crtinfo.CrtName = "test_server.crt"
    crtinfo.KeyName = "test_server.key"
    crtinfo.Names = []pkix.AttributeTypeAndValue{{asn1.ObjectIdentifier{2,1,3},"MAC_ADDR"}} //添加扩展字段用来做自定义使用

    crt,pri,err := Parse(baseinfo.CrtName,baseinfo.KeyName)
    if err != nil {
        t.Log("Parse crt error,err)
        return
    }
    err = CreateCRT(crt,crtinfo)
    if err != nil {
        t.Log("Create crt error,err)
    }
    os.Remove(baseinfo.CrtName)
    os.Remove(baseinfo.KeyName)
    os.Remove(crtinfo.CrtName)
    os.Remove(crtinfo.KeyName)
}