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Winni Neessen
580981b158
Centralized error definitions in `smtp/auth.go` and updated references in `auth_login.go` and `auth_plain.go`. This improves code maintainability and error consistency across the package.
76 lines
2.8 KiB
Go
76 lines
2.8 KiB
Go
// SPDX-FileCopyrightText: Copyright (c) 2022-2024 The go-mail Authors
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//
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// SPDX-License-Identifier: MIT
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package smtp
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import (
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"fmt"
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)
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// loginAuth is the type that satisfies the Auth interface for the "SMTP LOGIN" auth
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type loginAuth struct {
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username, password string
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host string
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respStep uint8
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}
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// LoginAuth returns an [Auth] that implements the LOGIN authentication
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// mechanism as it is used by MS Outlook. The Auth works similar to PLAIN
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// but instead of sending all in one response, the login is handled within
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// 3 steps:
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// - Sending AUTH LOGIN (server might responds with "Username:")
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// - Sending the username (server might responds with "Password:")
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// - Sending the password (server authenticates)
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// This is the common approach as specified by Microsoft in their MS-XLOGIN spec.
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// See: https://msopenspecs.azureedge.net/files/MS-XLOGIN/%5bMS-XLOGIN%5d.pdf
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// Yet, there is also an old IETF draft for SMTP AUTH LOGIN that states for clients:
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// "The contents of both challenges SHOULD be ignored.".
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// See: https://datatracker.ietf.org/doc/html/draft-murchison-sasl-login-00
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// Since there is no official standard RFC and we've seen different implementations
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// of this mechanism (sending "Username:", "Username", "username", "User name", etc.)
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// we follow the IETF-Draft and ignore any server challange to allow compatiblity
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// with most mail servers/providers.
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//
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// LoginAuth will only send the credentials if the connection is using TLS
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// or is connected to localhost. Otherwise authentication will fail with an
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// error, without sending the credentials.
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func LoginAuth(username, password, host string) Auth {
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return &loginAuth{username, password, host, 0}
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}
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// Start begins the SMTP authentication process by validating server's TLS status and hostname.
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// Returns "LOGIN" on success.
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func (a *loginAuth) Start(server *ServerInfo) (string, []byte, error) {
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// Must have TLS, or else localhost server.
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// Note: If TLS is not true, then we can't trust ANYTHING in ServerInfo.
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// In particular, it doesn't matter if the server advertises LOGIN auth.
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// That might just be the attacker saying
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// "it's ok, you can trust me with your password."
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if !server.TLS && !isLocalhost(server.Name) {
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return "", nil, ErrUnencrypted
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}
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if server.Name != a.host {
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return "", nil, ErrWrongHostname
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}
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a.respStep = 0
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return "LOGIN", nil, nil
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}
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// Next processes responses from the server during the SMTP authentication exchange, sending the
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// username and password.
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func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
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if more {
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switch a.respStep {
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case 0:
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a.respStep++
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return []byte(a.username), nil
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case 1:
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a.respStep++
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return []byte(a.password), nil
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default:
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return nil, fmt.Errorf("%w: %s", ErrUnexpectedServerResponse, string(fromServer))
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}
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}
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return nil, nil
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}
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