| // Copyright 2020 Google LLC. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // Package dca contains utils for implementing Device Certificate |
| // Authentication according to https://google.aip.dev/auth/4114 |
| // |
| // 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. |
| // |
| // 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 dca |
| |
| import ( |
| "net/url" |
| "os" |
| "strings" |
| |
| "google.golang.org/api/internal" |
| "google.golang.org/api/transport/cert" |
| ) |
| |
| const ( |
| mTLSModeAlways = "always" |
| mTLSModeNever = "never" |
| mTLSModeAuto = "auto" |
| ) |
| |
| // 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 *internal.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 |
| } |
| return clientCertSource, endpoint, 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 *internal.DialSettings) (cert.Source, error) { |
| if !isClientCertificateEnabled() { |
| return nil, nil |
| } else if settings.HTTPClient != nil { |
| return nil, nil // HTTPClient is incompatible with ClientCertificateSource |
| } 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 *internal.DialSettings, clientCertSource cert.Source) (string, error) { |
| if settings.Endpoint == "" { |
| mtlsMode := getMTLSMode() |
| if mtlsMode == mTLSModeAlways || (clientCertSource != nil && mtlsMode == mTLSModeAuto) { |
| return settings.DefaultMTLSEndpoint, nil |
| } |
| return settings.DefaultEndpoint, nil |
| } |
| if strings.Contains(settings.Endpoint, "://") { |
| // User passed in a full URL path, use it verbatim. |
| return settings.Endpoint, nil |
| } |
| if settings.DefaultEndpoint == "" { |
| // 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(settings.DefaultEndpoint, settings.Endpoint) |
| } |
| |
| 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(base, newHost string) (string, error) { |
| u, err := url.Parse(base) |
| if err != nil { |
| return "", err |
| } |
| u.Host = newHost |
| return u.String(), nil |
| } |