From b4a6cf4c7842dc9f62c3eec34fbbf947349f729d Mon Sep 17 00:00:00 2001
From: ale <ale@incal.net>
Date: Tue, 28 Sep 2021 22:19:08 +0100
Subject: [PATCH] Fix SMTP authentication
Provide our own net/smtp.Auth implementation to do AUTH PLAIN without
the TLS check.
Fixes issue #1.
---
protocol/smtp/smtp.go | 34 +++++++++++++++++++++++++++++++++-
1 file changed, 33 insertions(+), 1 deletion(-)
diff --git a/protocol/smtp/smtp.go b/protocol/smtp/smtp.go
index 92b931c..f57970a 100644
--- a/protocol/smtp/smtp.go
+++ b/protocol/smtp/smtp.go
@@ -58,7 +58,7 @@ func (c *Conn) Close() error {
}
func (c *Conn) SendMail(username, password, from string, to []string, msg []byte) error {
- auth := smtp.PlainAuth("", username, password, c.hostname)
+ auth := newPlainAuth("", username, password, c.hostname)
if ok, _ := c.client.Extension("AUTH"); !ok {
return errors.New("server does not support AUTH extension")
}
@@ -86,3 +86,35 @@ func (c *Conn) SendMail(username, password, from string, to []string, msg []byte
}
return nil
}
+
+// This is almost a copy of net/smtp/auth.go, but without the TLS
+// check. The net/smtp package attempts to autodetect TLS usage by
+// checking if the net.Conn it got is actually a *tls.Conn. Since we
+// wrap our connection in the logging wrapper, this check fails, and
+// net/smtp.PlainAuth will refuse to authenticate, thinking the
+// connection is unencrypted.
+type plainAuth struct {
+ identity, username, password string
+ host string
+}
+
+func newPlainAuth(identity, username, password, host string) smtp.Auth {
+ return &plainAuth{identity, username, password, host}
+}
+
+func (a *plainAuth) Start(server *smtp.ServerInfo) (string, []byte, error) {
+ // We know we have TLS.
+ if server.Name != a.host {
+ return "", nil, errors.New("wrong host name")
+ }
+ resp := []byte(a.identity + "\x00" + a.username + "\x00" + a.password)
+ return "PLAIN", resp, nil
+}
+
+func (a *plainAuth) Next(fromServer []byte, more bool) ([]byte, error) {
+ if more {
+ // We've already sent everything.
+ return nil, errors.New("unexpected server challenge")
+ }
+ return nil, nil
+}
--
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