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package email
import (
"errors"
"fmt"
"net/smtp"
)
type loginAuth struct {
host string
user string
pass string
}
// LoginAuth implements the LOGIN authentication mechanism.
//
// Adapted from smtp.PlainAuth in the standard library.
func LoginAuth(user, pass, host string) smtp.Auth {
return &loginAuth{host: host, user: user, pass: pass}
}
func isLocalhost(name string) bool {
return name == "localhost" || name == "127.0.0.1" || name == "::1"
}
func (a *loginAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
// Must have TLS, or else localhost server.
// Note: If TLS is not true, then we can't trust ANYTHING in ServerInfo.
// In particular, it doesn't matter if the server advertises PLAIN auth.
// That might just be the attacker saying
// "it's ok, you can trust me with your password."
if !server.TLS && !isLocalhost(server.Name) {
return "", nil, errors.New("unencrypted connection")
}
if server.Name != a.host {
return "", nil, errors.New("wrong host name")
}
return "LOGIN", nil, nil
}
func (a *loginAuth) Next(fromServer []byte, more bool) ([]byte, error) {
if !more {
return nil, nil
}
switch string(fromServer) {
case "Username:":
return []byte(a.user), nil
case "Password:":
return []byte(a.pass), nil
}
return nil, fmt.Errorf("unexpected server challenge: %s", string(fromServer))
}
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