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config.go
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config.go
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// Package tlsconfig provides opintionated helpers for building tls.Configs.
// It keeps up to date with internal CloudFoundry best practices and external
// industry best practices.
package tlsconfig
import (
"crypto/tls"
"crypto/x509"
"fmt"
)
// Config represents a half configured TLS configuration. It can be made usable
// by calling either of its two methods.
type Config struct {
opts []TLSOption
}
// TLSOption can be used to configure a TLS configuration for both clients and
// servers.
type TLSOption func(*tls.Config) error
// ServerOption can be used to configure a TLS configuration for a server.
type ServerOption func(*tls.Config) error
// ClientOption can be used to configure a TLS configuration for a client.
type ClientOption func(*tls.Config) error
// Build creates a half configured TLS configuration.
func Build(opts ...TLSOption) Config {
return Config{
opts: opts,
}
}
// Server can be used to build a TLS configuration suitable for servers (GRPC,
// HTTP, etc.). The options are applied in order. It is possible for a later
// option to undo the configuration that an earlier one applied. Care must be
// taken.
func (c Config) Server(opts ...ServerOption) (*tls.Config, error) {
config := &tls.Config{}
for _, opt := range c.opts {
if err := opt(config); err != nil {
return nil, err
}
}
for _, opt := range opts {
if err := opt(config); err != nil {
return nil, err
}
}
return config, nil
}
// Client can be used to build a TLS configuration suitable for clients (GRPC,
// HTTP, etc.). The options are applied in order. It is possible for a later
// option to undo the configuration that an earlier one applied. Care must be
// taken.
func (c Config) Client(opts ...ClientOption) (*tls.Config, error) {
config := &tls.Config{}
for _, opt := range c.opts {
if err := opt(config); err != nil {
return nil, err
}
}
for _, opt := range opts {
if err := opt(config); err != nil {
return nil, err
}
}
return config, nil
}
// WithExternalServiceDefaults modifies a *tls.Config that is suitable for use
// in communication between clients and servers where we do not control one end
// of the connection. It is less strict than the WithInternalServiceDefaults
// helper.
//
// The standards here are taken from the Mozilla SSL configuration generator
// set to "Intermediate" on Dec 19, 2019.
func WithExternalServiceDefaults() TLSOption {
return func(c *tls.Config) error {
c.MinVersion = tls.VersionTLS12
c.MaxVersion = tls.VersionTLS13
c.CipherSuites = []uint16{
tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
}
return nil
}
}
// WithInternalServiceDefaults modifies a *tls.Config that is suitable for use
// in communication links between internal services. It is not guaranteed to be
// suitable for communication to other external services as it contains a
// strict definition of acceptable standards.
//
// The standards were taken from the "Consolidated Remarks" internal document
// from Pivotal. The one exception to this is the use of the P256 curve in
// order to support gRPC clients which hardcode this configuration.
//
// Note: Due to the aggressive nature of the ciphersuites chosen here (they do
// not support any ECC signing) it is not possible to use ECC keys with this
// option.
func WithInternalServiceDefaults() TLSOption {
return func(c *tls.Config) error {
c.MinVersion = tls.VersionTLS12
c.MaxVersion = tls.VersionTLS13
c.CipherSuites = []uint16{
tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
}
return nil
}
}
// WithIdentity sets the identity of the server or client which will be
// presented to its peer upon connection.
func WithIdentity(cert tls.Certificate) TLSOption {
return func(c *tls.Config) error {
fail := func(err error) error {
return fmt.Errorf("failed to load keypair: %s", err.Error())
}
x509Cert, err := x509.ParseCertificate(cert.Certificate[0])
if err != nil {
return fail(err)
}
err = checkExpiration(x509Cert)
if err != nil {
return fail(err)
}
c.Certificates = []tls.Certificate{cert}
return nil
}
}
// WithIdentityFromFile sets the identity of the server or client which will be
// presented to its peer upon connection from provided cert and key files.
func WithIdentityFromFile(certPath string, keyPath string) TLSOption {
return func(c *tls.Config) error {
cert, err := tls.LoadX509KeyPair(certPath, keyPath)
if err != nil {
return fmt.Errorf("failed to load keypair: %s", err.Error())
}
return WithIdentity(cert)(c)
}
}
// WithClientAuthentication makes the server verify that all clients present an
// identity that can be validated by the certificate pool provided.
func WithClientAuthentication(authority *x509.CertPool) ServerOption {
return func(c *tls.Config) error {
c.ClientAuth = tls.RequireAndVerifyClientCert
c.ClientCAs = authority
return nil
}
}
// WithClientAuthenticationBuilder uses the passed PoolBuilder to create the certificate
// pool to use as the authority when verifying client certificates.
func WithClientAuthenticationBuilder(builder PoolBuilder) ServerOption {
return func(c *tls.Config) error {
pool, err := builder.Build()
if err != nil {
return err
}
return WithClientAuthentication(pool)(c)
}
}
// WithClientAuthenticationFromFile makes the server verify that all clients present an
// identity that can be validated by the CA file provided.
func WithClientAuthenticationFromFile(caPath string) ServerOption {
return func(c *tls.Config) error {
return WithClientAuthenticationBuilder(
FromEmptyPool(
WithCertsFromFile(caPath),
),
)(c)
}
}
// WithAuthorityBuilder uses the passed PoolBuilder to create the certificate
// pool to use as the authority.
func WithAuthorityBuilder(builder PoolBuilder) ClientOption {
return func(c *tls.Config) error {
pool, err := builder.Build()
if err != nil {
return err
}
return WithAuthority(pool)(c)
}
}
// WithAuthority makes the client verify that the server presents an identity
// that can be validated by the certificate pool provided.
func WithAuthority(authority *x509.CertPool) ClientOption {
return func(c *tls.Config) error {
c.RootCAs = authority
return nil
}
}
// WithAuthorityFromFile makes the client verify that the server presents an identity
// that can be validated by the CA file provided.
func WithAuthorityFromFile(caPath string) ClientOption {
return func(c *tls.Config) error {
return WithAuthorityBuilder(
FromEmptyPool(
WithCertsFromFile(caPath),
),
)(c)
}
}
// WithServerName makes the client verify that the server name in the
// certificate presented by the server.
func WithServerName(name string) ClientOption {
return func(c *tls.Config) error {
c.ServerName = name
return nil
}
}