feat(terraform): Add hyphen and non-ASCII support for domain names in…

… credential extraction (#6108)

Co-authored-by: simar7 <1254783+simar7@users.noreply.github.com>

docs/docs/scanner/misconfiguration/index.md

@@ -360,6 +360,25 @@ This can be repeated for specifying multiple packages.
 trivy conf --policy ./policy --namespaces main --namespaces user ./configs
 ```
 
+### Private terraform registries
+Trivy can download terraform code from private registries.
+To pass credentials you must use the `TF_TOKEN_` environment variables.
+You cannot use a `.terraformrc` or `terraform.rc` file, these are not supported by trivy yet.
+
+From the terraform docs:
+
+> Environment variable names should have the prefix TF_TOKEN_ added to the domain name, with periods encoded as underscores.
+> For example, the value of a variable named `TF_TOKEN_app_terraform_io` will be used as a bearer authorization token when the CLI makes service requests to the hostname `app.terraform.io`.
+>
+> You must convert domain names containing non-ASCII characters to their punycode equivalent with an ACE prefix.
+> For example, token credentials for `例えば.com` must be set in a variable called `TF_TOKEN_xn--r8j3dr99h_com`.
+>
+> Hyphens are also valid within host names but usually invalid as variable names and may be encoded as double underscores.
+> For example, you can set a token for the domain name café.fr as TF_TOKEN_xn--caf-dma_fr or TF_TOKEN_xn____caf__dma_fr.
+
+If multiple variables evaluate to the same hostname, Trivy will choose the environment variable name where the dashes have not been encoded as double underscores.
+
+
 ### Skipping resources by inline comments
 Some configuration file formats (e.g. Terraform) support inline comments.
 

pkg/iac/scanners/terraform/parser/resolvers/registry.go

@@ -11,6 +11,8 @@ import (
 	"strings"
 	"time"
 
+	"golang.org/x/net/idna"
+
 	"github.com/aquasecurity/go-version/pkg/semver"
 )
 
@@ -55,12 +57,11 @@ func (r *registryResolver) Resolve(ctx context.Context, target fs.FS, opt Option
 		hostname = parts[0]
 		parts = parts[1:]
 
-		envVar := fmt.Sprintf("TF_TOKEN_%s", strings.ReplaceAll(hostname, ".", "_"))
-		token = os.Getenv(envVar)
-		if token != "" {
+		token, err = getPrivateRegistryTokenFromEnvVars(hostname)
+		if err == nil {
 			opt.Debug("Found a token for the registry at %s", hostname)
 		} else {
-			opt.Debug("No token was found for the registry at %s", hostname)
+			opt.Debug(err.Error())
 		}
 	}
 
@@ -136,6 +137,28 @@ func (r *registryResolver) Resolve(ctx context.Context, target fs.FS, opt Option
 	return filesystem, prefix, downloadPath, true, nil
 }
 
+func getPrivateRegistryTokenFromEnvVars(hostname string) (string, error) {
+	token := ""
+	asciiHostname, err := idna.ToASCII(hostname)
+	if err != nil {
+		return "", fmt.Errorf("could not convert hostname %s to a punycode encoded ASCII string so cannot find token for this registry", hostname)
+	}
+
+	envVar := fmt.Sprintf("TF_TOKEN_%s", strings.ReplaceAll(asciiHostname, ".", "_"))
+	token = os.Getenv(envVar)
+
+	// Dashes in the hostname can optionally be converted to double underscores
+	if token == "" {
+		envVar = strings.ReplaceAll(envVar, "-", "__")
+		token = os.Getenv(envVar)
+	}
+
+	if token == "" {
+		return "", fmt.Errorf("no token was found for the registry at %s", hostname)
+	}
+	return token, nil
+}
+
 func resolveVersion(input string, versions moduleVersions) (string, error) {
 	if len(versions.Modules) != 1 {
 		return "", fmt.Errorf("1 module expected, found %d", len(versions.Modules))

pkg/iac/scanners/terraform/parser/resolvers/registry_test.go

@@ -0,0 +1,56 @@
+package resolvers
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func Test_getPrivateRegistryTokenFromEnvVars_ErrorsWithNoEnvVarSet(t *testing.T) {
+	token, err := getPrivateRegistryTokenFromEnvVars("registry.example.com")
+	assert.Equal(t, "", token)
+	assert.Equal(t, "no token was found for the registry at registry.example.com", err.Error())
+}
+
+func Test_getPrivateRegistryTokenFromEnvVars_ConvertsSiteNameToEnvVar(t *testing.T) {
+	tests := []struct {
+		name      string
+		siteName  string
+		tokenName string
+	}{
+		{
+			name:      "returns string when simple env var set",
+			siteName:  "registry.example.com",
+			tokenName: "TF_TOKEN_registry_example_com",
+		},
+		{
+			name:      "allows dashes in hostname to be dashes",
+			siteName:  "my-registry.example.com",
+			tokenName: "TF_TOKEN_my-registry_example_com",
+		},
+		{
+			name:      "allows dashes in hostname to be double underscores",
+			siteName:  "my-registry.example.com",
+			tokenName: "TF_TOKEN_my__registry_example_com",
+		},
+		{
+			name:      "handles utf8 to punycode correctly",
+			siteName:  "例えば.com",
+			tokenName: "TF_TOKEN_xn--r8j3dr99h_com",
+		},
+		{
+			name:      "handles punycode with dash to underscore conversion",
+			siteName:  "café.fr",
+			tokenName: "TF_TOKEN_xn____caf__dma_fr",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Setenv(tt.tokenName, "abcd")
+			token, err := getPrivateRegistryTokenFromEnvVars(tt.siteName)
+			assert.Equal(t, "abcd", token)
+			assert.Equal(t, nil, err)
+		})
+	}
+}