Fix http auth header parsing (#34936)

Using `strings.EqualFold` is wrong in many cases.

modules/auth/httpauth/httpauth.go

@@ -0,0 +1,47 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package httpauth
+
+import (
+	"encoding/base64"
+	"strings"
+
+	"code.gitea.io/gitea/modules/util"
+)
+
+type BasicAuth struct {
+	Username, Password string
+}
+
+type BearerToken struct {
+	Token string
+}
+
+type ParsedAuthorizationHeader struct {
+	BasicAuth   *BasicAuth
+	BearerToken *BearerToken
+}
+
+func ParseAuthorizationHeader(header string) (ret ParsedAuthorizationHeader, _ bool) {
+	parts := strings.Fields(header)
+	if len(parts) != 2 {
+		return ret, false
+	}
+	if util.AsciiEqualFold(parts[0], "basic") {
+		s, err := base64.StdEncoding.DecodeString(parts[1])
+		if err != nil {
+			return ret, false
+		}
+		u, p, ok := strings.Cut(string(s), ":")
+		if !ok {
+			return ret, false
+		}
+		ret.BasicAuth = &BasicAuth{Username: u, Password: p}
+		return ret, true
+	} else if util.AsciiEqualFold(parts[0], "token") || util.AsciiEqualFold(parts[0], "bearer") {
+		ret.BearerToken = &BearerToken{Token: parts[1]}
+		return ret, true
+	}
+	return ret, false
+}