feat: open proxy token file

proto.go

@@ -1,8 +1,10 @@
 package main
 
 import (
+	"fmt"
 	"os"
 	"strconv"
+	"strings"
 )
 
 const (
@@ -20,8 +22,26 @@ func envAddr() string {
 	return defaultAddr
 }
 
-func envToken() string {
-	return os.Getenv("OPEN_PROXY_TOKEN")
+func envToken() (string, error) {
+	if v := os.Getenv("OPEN_PROXY_TOKEN"); v != "" {
+		return v, nil
+	}
+
+	path := os.Getenv("OPEN_PROXY_TOKEN_FILE")
+	if path == "" {
+		return "", nil
+	}
+
+	b, err := os.ReadFile(path)
+	if err != nil {
+		return "", fmt.Errorf("read OPEN_PROXY_TOKEN_FILE %q: %w", path, err)
+	}
+
+	token := strings.TrimRight(string(b), "\r\n")
+	if token == "" {
+		return "", fmt.Errorf("OPEN_PROXY_TOKEN_FILE %q is empty", path)
+	}
+	return token, nil
 }
 
 func envMaxSize() int64 {