feat: secret resolution (literal, env, file)

secrets.go

@@ -0,0 +1,37 @@
+package traefikllmgateway
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+// resolveSecret resolves a config string value to its underlying secret. An
+// empty value returns empty with no error. A "env:NAME" value returns
+// os.Getenv(NAME), erroring if the variable is unset or empty. A
+// "file:/path" value returns the file's contents with surrounding
+// whitespace trimmed, erroring if the file cannot be read. Any other value
+// is returned unchanged as a literal.
+//
+// Error messages never include a resolved secret value — only the env var
+// name or file path, which are config, not secrets.
+func resolveSecret(v string) (string, error) {
+	if v == "" {
+		return "", nil
+	}
+	if name, ok := strings.CutPrefix(v, "env:"); ok {
+		val := os.Getenv(name)
+		if val == "" {
+			return "", fmt.Errorf("llmgateway: env var %q is unset or empty", name)
+		}
+		return val, nil
+	}
+	if path, ok := strings.CutPrefix(v, "file:"); ok {
+		b, err := os.ReadFile(path)
+		if err != nil {
+			return "", fmt.Errorf("llmgateway: cannot read secret file %q: %w", path, err)
+		}
+		return strings.TrimSpace(string(b)), nil
+	}
+	return v, nil
+}

secrets_test.go

@@ -0,0 +1,37 @@
+package traefikllmgateway
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestResolveSecret(t *testing.T) {
+	t.Setenv("LLMGW_T", "from-env")
+	dir := t.TempDir()
+	fp := filepath.Join(dir, "k")
+	if err := os.WriteFile(fp, []byte("from-file\n"), 0o600); err != nil {
+		t.Fatalf("WriteFile: %v", err)
+	}
+
+	cases := []struct {
+		in      string
+		want    string
+		wantErr bool
+	}{
+		{"plain", "plain", false},
+		{"env:LLMGW_T", "from-env", false},
+		{"env:LLMGW_MISSING", "", true},
+		{"file:" + fp, "from-file", false},
+		{"file:" + fp + ".nope", "", true},
+		{"", "", false},
+	}
+	for _, c := range cases {
+		t.Run(c.in, func(t *testing.T) {
+			got, err := resolveSecret(c.in)
+			if (err != nil) != c.wantErr || got != c.want {
+				t.Errorf("resolveSecret(%q) = %q, %v; wantErr %v", c.in, got, err, c.wantErr)
+			}
+		})
+	}
+}