Auth Proxy: encoding of non-ASCII headers (#44797)

* Decode auth proxy headers using URL encoding

* Header encoding configuration via settings file

* Rename configuration setting to headers_encoded

* Quoted-printable encoding

* Tests for AuthProxy

* Fix encoding name

* Remove authproxy init

pkg/util/encoding.go

@@ -6,6 +6,8 @@ import (
 	"encoding/base64"
 	"encoding/hex"
 	"errors"
+	"io"
+	"mime/quotedprintable"
 	"strings"
 
 	"golang.org/x/crypto/pbkdf2"
@@ -71,3 +73,12 @@ func RandomHex(n int) (string, error) {
 	}
 	return hex.EncodeToString(bytes), nil
 }
+
+// decodeQuotedPrintable decodes quoted-printable UTF-8 string
+func DecodeQuotedPrintable(encodedValue string) string {
+	decodedBytes, err := io.ReadAll(quotedprintable.NewReader(strings.NewReader(encodedValue)))
+	if err != nil {
+		return encodedValue
+	}
+	return string(decodedBytes)
+}