google: add warning about externally-provided credentials

Change-Id: Ic2ce6e9c3ed735f4fc6d78a22cf0d5e95fca91a1
Reviewed-on: https://go-review.googlesource.com/c/oauth2/+/643158
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Sai Sunder Srinivasan <saisunder@google.com>
Run-TryBot: Cody Oss <codyoss@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cody Oss <codyoss@google.com>

google/default.go

@@ -251,6 +251,12 @@ func FindDefaultCredentials(ctx context.Context, scopes ...string) (*Credentials
 // a Google Developers service account key file, a gcloud user credentials file (a.k.a. refresh
 // token JSON), or the JSON configuration file for workload identity federation in non-Google cloud
 // platforms (see https://cloud.google.com/iam/docs/how-to#using-workload-identity-federation).
+//
+// Important: If you accept a credential configuration (credential JSON/File/Stream) from an
+// external source for authentication to Google Cloud Platform, you must validate it before
+// providing it to any Google API or library. Providing an unvalidated credential configuration to
+// Google APIs can compromise the security of your systems and data. For more information, refer to
+// [Validate credential configurations from external sources](https://cloud.google.com/docs/authentication/external/externally-sourced-credentials).
 func CredentialsFromJSONWithParams(ctx context.Context, jsonData []byte, params CredentialsParams) (*Credentials, error) {
 	// Make defensive copy of the slices in params.
 	params = params.deepCopy()
@@ -294,6 +300,12 @@ func CredentialsFromJSONWithParams(ctx context.Context, jsonData []byte, params
 }
 
 // CredentialsFromJSON invokes CredentialsFromJSONWithParams with the specified scopes.
+//
+// Important: If you accept a credential configuration (credential JSON/File/Stream) from an
+// external source for authentication to Google Cloud Platform, you must validate it before
+// providing it to any Google API or library. Providing an unvalidated credential configuration to
+// Google APIs can compromise the security of your systems and data. For more information, refer to
+// [Validate credential configurations from external sources](https://cloud.google.com/docs/authentication/external/externally-sourced-credentials).
 func CredentialsFromJSON(ctx context.Context, jsonData []byte, scopes ...string) (*Credentials, error) {
 	var params CredentialsParams
 	params.Scopes = scopes

google/externalaccount/basecredentials.go

@@ -278,20 +278,52 @@ type Format struct {
 type CredentialSource struct {
 	// File is the location for file sourced credentials.
 	// One field amongst File, URL, Executable, or EnvironmentID should be provided, depending on the kind of credential in question.
+	//
+	// Important: If you accept a credential configuration (credential
+	// JSON/File/Stream) from an external source for authentication to Google
+	// Cloud Platform, you must validate it before providing it to any Google
+	// API or library. Providing an unvalidated credential configuration to
+	// Google APIs can compromise the security of your systems and data. For
+	// more information, refer to [Validate credential configurations from
+	// external sources](https://cloud.google.com/docs/authentication/external/externally-sourced-credentials).
 	File string `json:"file"`
 
 	// Url is the URL to call for URL sourced credentials.
 	// One field amongst File, URL, Executable, or EnvironmentID should be provided, depending on the kind of credential in question.
+	//
+	// Important: If you accept a credential configuration (credential
+	// JSON/File/Stream) from an external source for authentication to Google
+	// Cloud Platform, you must validate it before providing it to any Google
+	// API or library. Providing an unvalidated credential configuration to
+	// Google APIs can compromise the security of your systems and data. For
+	// more information, refer to [Validate credential configurations from
+	// external sources](https://cloud.google.com/docs/authentication/external/externally-sourced-credentials).
 	URL string `json:"url"`
 	// Headers are the headers to attach to the request for URL sourced credentials.
 	Headers map[string]string `json:"headers"`
 
 	// Executable is the configuration object for executable sourced credentials.
 	// One field amongst File, URL, Executable, or EnvironmentID should be provided, depending on the kind of credential in question.
+	//
+	// Important: If you accept a credential configuration (credential
+	// JSON/File/Stream) from an external source for authentication to Google
+	// Cloud Platform, you must validate it before providing it to any Google
+	// API or library. Providing an unvalidated credential configuration to
+	// Google APIs can compromise the security of your systems and data. For
+	// more information, refer to [Validate credential configurations from
+	// external sources](https://cloud.google.com/docs/authentication/external/externally-sourced-credentials).
 	Executable *ExecutableConfig `json:"executable"`
 
 	// EnvironmentID is the EnvironmentID used for AWS sourced credentials. This should start with "AWS".
 	// One field amongst File, URL, Executable, or EnvironmentID should be provided, depending on the kind of credential in question.
+	//
+	// Important: If you accept a credential configuration (credential
+	// JSON/File/Stream) from an external source for authentication to Google
+	// Cloud Platform, you must validate it before providing it to any Google
+	// API or library. Providing an unvalidated credential configuration to
+	// Google APIs can compromise the security of your systems and data. For
+	// more information, refer to [Validate credential configurations from
+	// external sources](https://cloud.google.com/docs/authentication/external/externally-sourced-credentials).
 	EnvironmentID string `json:"environment_id"`
 	// RegionURL is the metadata URL to retrieve the region from for EC2 AWS credentials.
 	RegionURL string `json:"region_url"`