Add GCS source support for modules

configs/configload/getter.go

@@ -20,6 +20,7 @@ import (
 var goGetterDetectors = []getter.Detector{
 	new(getter.GitHubDetector),
 	new(getter.BitBucketDetector),
+	new(getter.GCSDetector),
 	new(getter.S3Detector),
 	new(getter.FileDetector),
 }
@@ -44,6 +45,7 @@ var goGetterDecompressors = map[string]getter.Decompressor{
 
 var goGetterGetters = map[string]getter.Getter{
 	"file":  new(getter.FileGetter),
+	"gcs":   new(getter.GCSGetter),
 	"git":   new(getter.GitGetter),
 	"hg":    new(getter.HgGetter),
 	"s3":    new(getter.S3Getter),

internal/initwd/getter.go

@@ -22,6 +22,7 @@ import (
 var goGetterDetectors = []getter.Detector{
 	new(getter.GitHubDetector),
 	new(getter.BitBucketDetector),
+	new(getter.GCSDetector),
 	new(getter.S3Detector),
 	new(getter.FileDetector),
 }
@@ -46,6 +47,7 @@ var goGetterDecompressors = map[string]getter.Decompressor{
 
 var goGetterGetters = map[string]getter.Getter{
 	"file":  new(getter.FileGetter),
+	"gcs":   new(getter.GCSGetter),
 	"git":   new(getter.GitGetter),
 	"hg":    new(getter.HgGetter),
 	"s3":    new(getter.S3Getter),

website/docs/modules/sources.html.markdown

@@ -31,6 +31,8 @@ types, as listed below.
 
   * [S3 buckets](#s3-bucket)
 
+  * [GCS buckets](#gcs-bucket)
+
 Each of these is described in the following sections. Module source addresses
 use a _URL-like_ syntax, but with extensions to support unambiguous selection
 of sources and additional features.
@@ -375,6 +377,30 @@ preferring those earlier in the list when multiple are available:
 * If running on an EC2 instance, temporary credentials associated with the
   instance's IAM Instance Profile.
 
+## GCS Bucket
+
+You can use archives stored in Google Cloud Storage as module sources using the special `gcs::`
+prefix, followed by
+[a GCS bucket object URL](https://cloud.google.com/storage/docs/request-endpoints#typical).
+
+For example
+
+* `gcs::https://www.googleapis.com/storage/v1/BUCKET_NAME/PATH_TO_MODULE`
+* `gcs::https://www.googleapis.com/storage/v1/BUCKET_NAME/PATH/TO/module.zip`
+
+```hcl
+module "consul" {
+  source = "gcs::https://www.googleapis.com/storage/v1/modules/foomodule.zip"
+}
+```
+
+The module installer uses Google Cloud SDK to authenticate with GCS. To set credentials you can:
+
+* Enter the path of your service account key file in the GOOGLE_APPLICATION_CREDENTIALS environment variable, or;
+* If you're running Terraform from a GCE instance, default credentials are automatically available. See [Creating and Enabling Service Accounts](https://cloud.google.com/compute/docs/authentication) for Instances for more details
+* On your computer, you can make your Google identity available by running `gcloud auth application-default login`.
+
+
 ## Modules in Package Sub-directories
 
 When the source of a module is a version control repository or archive file