peridot/vendor/google.golang.org/api/internal/cba.go

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// Copyright 2020 Google LLC.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// cba.go (certificate-based access) contains utils for implementing Device Certificate
// Authentication according to https://google.aip.dev/auth/4114 and Default Credentials
// for Google Cloud Virtual Environments according to https://google.aip.dev/auth/4115.
//
// The overall logic for DCA is as follows:
// 1. If both endpoint override and client certificate are specified, use them as is.
// 2. If user does not specify client certificate, we will attempt to use default
// client certificate.
// 3. If user does not specify endpoint override, we will use defaultMtlsEndpoint if
// client certificate is available and defaultEndpoint otherwise.
//
// Implications of the above logic:
// 1. If the user specifies a non-mTLS endpoint override but client certificate is
// available, we will pass along the cert anyway and let the server decide what to do.
// 2. If the user specifies an mTLS endpoint override but client certificate is not
// available, we will not fail-fast, but let backend throw error when connecting.
//
// If running within Google's cloud environment, and client certificate is not specified
// and not available through DCA, we will try mTLS with credentials held by
// the Secure Session Agent, which is part of Google's cloud infrastructure.
//
// We would like to avoid introducing client-side logic that parses whether the
// endpoint override is an mTLS url, since the url pattern may change at anytime.
//
// This package is not intended for use by end developers. Use the
// google.golang.org/api/option package to configure API clients.
// Package internal supports the options and transport packages.
package internal
import (
"context"
"crypto/tls"
"errors"
"net"
"net/url"
"os"
"strings"
"github.com/google/s2a-go"
"github.com/google/s2a-go/fallback"
"google.golang.org/api/internal/cert"
"google.golang.org/grpc/credentials"
)
const (
mTLSModeAlways = "always"
mTLSModeNever = "never"
mTLSModeAuto = "auto"
// Experimental: if true, the code will try MTLS with S2A as the default for transport security. Default value is false.
googleAPIUseS2AEnv = "EXPERIMENTAL_GOOGLE_API_USE_S2A"
universeDomainPlaceholder = "UNIVERSE_DOMAIN"
)
var (
errUniverseNotSupportedMTLS = errors.New("mTLS is not supported in any universe other than googleapis.com")
)
// getClientCertificateSourceAndEndpoint is a convenience function that invokes
// getClientCertificateSource and getEndpoint sequentially and returns the client
// cert source and endpoint as a tuple.
func getClientCertificateSourceAndEndpoint(settings *DialSettings) (cert.Source, string, error) {
clientCertSource, err := getClientCertificateSource(settings)
if err != nil {
return nil, "", err
}
endpoint, err := getEndpoint(settings, clientCertSource)
if err != nil {
return nil, "", err
}
// TODO(chrisdsmith): https://github.com/googleapis/google-api-go-client/issues/2359
if settings.Endpoint == "" && !settings.IsUniverseDomainGDU() && settings.DefaultEndpointTemplate != "" {
// TODO(chrisdsmith): https://github.com/googleapis/google-api-go-client/issues/2359
// if settings.DefaultEndpointTemplate == "" {
// return nil, "", errors.New("internaloption.WithDefaultEndpointTemplate is required if option.WithUniverseDomain is not googleapis.com")
// }
endpoint = resolvedDefaultEndpoint(settings)
}
return clientCertSource, endpoint, nil
}
type transportConfig struct {
clientCertSource cert.Source // The client certificate source.
endpoint string // The corresponding endpoint to use based on client certificate source.
s2aAddress string // The S2A address if it can be used, otherwise an empty string.
s2aMTLSEndpoint string // The MTLS endpoint to use with S2A.
}
func getTransportConfig(settings *DialSettings) (*transportConfig, error) {
clientCertSource, endpoint, err := getClientCertificateSourceAndEndpoint(settings)
if err != nil {
return nil, err
}
defaultTransportConfig := transportConfig{
clientCertSource: clientCertSource,
endpoint: endpoint,
s2aAddress: "",
s2aMTLSEndpoint: "",
}
if !shouldUseS2A(clientCertSource, settings) {
return &defaultTransportConfig, nil
}
if !settings.IsUniverseDomainGDU() {
return nil, errUniverseNotSupportedMTLS
}
s2aAddress := GetS2AAddress()
if s2aAddress == "" {
return &defaultTransportConfig, nil
}
return &transportConfig{
clientCertSource: clientCertSource,
endpoint: endpoint,
s2aAddress: s2aAddress,
s2aMTLSEndpoint: settings.DefaultMTLSEndpoint,
}, nil
}
// getClientCertificateSource returns a default client certificate source, if
// not provided by the user.
//
// A nil default source can be returned if the source does not exist. Any exceptions
// encountered while initializing the default source will be reported as client
// error (ex. corrupt metadata file).
//
// Important Note: For now, the environment variable GOOGLE_API_USE_CLIENT_CERTIFICATE
// must be set to "true" to allow certificate to be used (including user provided
// certificates). For details, see AIP-4114.
func getClientCertificateSource(settings *DialSettings) (cert.Source, error) {
if !isClientCertificateEnabled() {
return nil, nil
} else if settings.ClientCertSource != nil {
return settings.ClientCertSource, nil
} else {
return cert.DefaultSource()
}
}
func isClientCertificateEnabled() bool {
useClientCert := os.Getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE")
// TODO(andyrzhao): Update default to return "true" after DCA feature is fully released.
return strings.ToLower(useClientCert) == "true"
}
// getEndpoint returns the endpoint for the service, taking into account the
// user-provided endpoint override "settings.Endpoint".
//
// If no endpoint override is specified, we will either return the default endpoint or
// the default mTLS endpoint if a client certificate is available.
//
// You can override the default endpoint choice (mtls vs. regular) by setting the
// GOOGLE_API_USE_MTLS_ENDPOINT environment variable.
//
// If the endpoint override is an address (host:port) rather than full base
// URL (ex. https://...), then the user-provided address will be merged into
// the default endpoint. For example, WithEndpoint("myhost:8000") and
// WithDefaultEndpoint("https://foo.com/bar/baz") will return "https://myhost:8080/bar/baz"
func getEndpoint(settings *DialSettings, clientCertSource cert.Source) (string, error) {
if settings.Endpoint == "" {
if isMTLS(clientCertSource) {
if !settings.IsUniverseDomainGDU() {
return "", errUniverseNotSupportedMTLS
}
return settings.DefaultMTLSEndpoint, nil
}
return resolvedDefaultEndpoint(settings), nil
}
if strings.Contains(settings.Endpoint, "://") {
// User passed in a full URL path, use it verbatim.
return settings.Endpoint, nil
}
if resolvedDefaultEndpoint(settings) == "" {
// If DefaultEndpoint is not configured, use the user provided endpoint verbatim.
// This allows a naked "host[:port]" URL to be used with GRPC Direct Path.
return settings.Endpoint, nil
}
// Assume user-provided endpoint is host[:port], merge it with the default endpoint.
return mergeEndpoints(resolvedDefaultEndpoint(settings), settings.Endpoint)
}
func isMTLS(clientCertSource cert.Source) bool {
mtlsMode := getMTLSMode()
return mtlsMode == mTLSModeAlways || (clientCertSource != nil && mtlsMode == mTLSModeAuto)
}
// resolvedDefaultEndpoint returns the DefaultEndpointTemplate merged with the
// Universe Domain if the DefaultEndpointTemplate is set, otherwise returns the
// deprecated DefaultEndpoint value.
func resolvedDefaultEndpoint(settings *DialSettings) string {
if settings.DefaultEndpointTemplate == "" {
return settings.DefaultEndpoint
}
return strings.Replace(settings.DefaultEndpointTemplate, universeDomainPlaceholder, settings.GetUniverseDomain(), 1)
}
func getMTLSMode() string {
mode := os.Getenv("GOOGLE_API_USE_MTLS_ENDPOINT")
if mode == "" {
mode = os.Getenv("GOOGLE_API_USE_MTLS") // Deprecated.
}
if mode == "" {
return mTLSModeAuto
}
return strings.ToLower(mode)
}
func mergeEndpoints(baseURL, newHost string) (string, error) {
u, err := url.Parse(fixScheme(baseURL))
if err != nil {
return "", err
}
return strings.Replace(baseURL, u.Host, newHost, 1), nil
}
func fixScheme(baseURL string) string {
if !strings.Contains(baseURL, "://") {
return "https://" + baseURL
}
return baseURL
}
// GetGRPCTransportConfigAndEndpoint returns an instance of credentials.TransportCredentials, and the
// corresponding endpoint to use for GRPC client.
func GetGRPCTransportConfigAndEndpoint(settings *DialSettings) (credentials.TransportCredentials, string, error) {
config, err := getTransportConfig(settings)
if err != nil {
return nil, "", err
}
defaultTransportCreds := credentials.NewTLS(&tls.Config{
GetClientCertificate: config.clientCertSource,
})
if config.s2aAddress == "" {
return defaultTransportCreds, config.endpoint, nil
}
var fallbackOpts *s2a.FallbackOptions
// In case of S2A failure, fall back to the endpoint that would've been used without S2A.
if fallbackHandshake, err := fallback.DefaultFallbackClientHandshakeFunc(config.endpoint); err == nil {
fallbackOpts = &s2a.FallbackOptions{
FallbackClientHandshakeFunc: fallbackHandshake,
}
}
s2aTransportCreds, err := s2a.NewClientCreds(&s2a.ClientOptions{
S2AAddress: config.s2aAddress,
FallbackOpts: fallbackOpts,
})
if err != nil {
// Use default if we cannot initialize S2A client transport credentials.
return defaultTransportCreds, config.endpoint, nil
}
return s2aTransportCreds, config.s2aMTLSEndpoint, nil
}
// GetHTTPTransportConfigAndEndpoint returns a client certificate source, a function for dialing MTLS with S2A,
// and the endpoint to use for HTTP client.
func GetHTTPTransportConfigAndEndpoint(settings *DialSettings) (cert.Source, func(context.Context, string, string) (net.Conn, error), string, error) {
config, err := getTransportConfig(settings)
if err != nil {
return nil, nil, "", err
}
if config.s2aAddress == "" {
return config.clientCertSource, nil, config.endpoint, nil
}
var fallbackOpts *s2a.FallbackOptions
// In case of S2A failure, fall back to the endpoint that would've been used without S2A.
if fallbackURL, err := url.Parse(config.endpoint); err == nil {
if fallbackDialer, fallbackServerAddr, err := fallback.DefaultFallbackDialerAndAddress(fallbackURL.Hostname()); err == nil {
fallbackOpts = &s2a.FallbackOptions{
FallbackDialer: &s2a.FallbackDialer{
Dialer: fallbackDialer,
ServerAddr: fallbackServerAddr,
},
}
}
}
dialTLSContextFunc := s2a.NewS2ADialTLSContextFunc(&s2a.ClientOptions{
S2AAddress: config.s2aAddress,
FallbackOpts: fallbackOpts,
})
return nil, dialTLSContextFunc, config.s2aMTLSEndpoint, nil
}
func shouldUseS2A(clientCertSource cert.Source, settings *DialSettings) bool {
// If client cert is found, use that over S2A.
if clientCertSource != nil {
return false
}
// If EXPERIMENTAL_GOOGLE_API_USE_S2A is not set to true, skip S2A.
if !isGoogleS2AEnabled() {
return false
}
// If DefaultMTLSEndpoint is not set or has endpoint override, skip S2A.
if settings.DefaultMTLSEndpoint == "" || settings.Endpoint != "" {
return false
}
// If custom HTTP client is provided, skip S2A.
if settings.HTTPClient != nil {
return false
}
return !settings.EnableDirectPath && !settings.EnableDirectPathXds
}
func isGoogleS2AEnabled() bool {
return strings.ToLower(os.Getenv(googleAPIUseS2AEnv)) == "true"
}