Add package for working with systemd credentials

credentials/credentials.go

@@ -0,0 +1,64 @@
+// Package credentials provides functions for working with systemd service credentials as documented by https://www.freedesktop.org/software/systemd/man/systemd.exec.html#Credentials.
+package credentials
+
+import (
+	"fmt"
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+func directory() (string, bool) {
+	return os.LookupEnv("CREDENTIALS_DIRECTORY")
+}
+
+// Available returns whether credentials are available to the process
+func Available() bool {
+	_, available := directory()
+	return available
+}
+
+// All returns a map of all available credentials
+func All() map[string]string {
+	dir, ok := directory()
+	if !ok {
+		return nil
+	}
+
+	filesystem := os.DirFS(dir)
+	matches, _ := fs.Glob(filesystem, "*")
+
+	creds := make(map[string]string)
+	for _, match := range matches {
+		data, _ := fs.ReadFile(filesystem, match)
+		str := strings.TrimRight(string(data), "\n")
+
+		basename := filepath.Base(match)
+		creds[basename] = str
+	}
+
+	return creds
+}
+
+// Get returns a credential for a specified name
+func Get(key string) (string, bool) {
+	creds := All()
+	cred, ok := creds[key]
+	return cred, ok
+}
+
+// AsEnvironment loads all available credentials into the process environment, prefixing
+// each credential name with SYSTEMD_CREDENTIAL_
+// Note that this may nullify some of the security benefits of using LoadCredential/SetCredential
+func AsEnvironment() error {
+	creds := All()
+
+	for key, value := range creds {
+		if err := os.Setenv("SYSTEMD_CREDENTIAL_"+key, value); err != nil {
+			return fmt.Errorf("error setting credential: %w", err)
+		}
+	}
+
+	return nil
+}