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[PATCH] Mail: allow auth to the proxy without auth to the backend

Arnout Engelen
September 19, 2023 06:30AM
# HG changeset patch
# User Arnout Engelen <arnout@bzzt.net>
# Date 1695027670 -7200
# Mon Sep 18 11:01:10 2023 +0200
# Node ID 9606e589b9537495c0457383048ac6888be0e7b4
# Parent daf8f5ba23d8e9955b22782d945f9c065f4b6baa
Mail: allow auth to the proxy without auth to the backend

Currently, when the client authenticates itself to the nginx
mail proxy, the mail proxy also authenticates itself to the
backend.

I encountered a situation where I wanted the proxy to require
authentication, and forward the mail to a (local/firewalled)
mailserver that does not have authentication configured. I
created the patch below to support that.

I'm providing this patch primarily for feedback at this point:
while it does work for my scenario and pass the nginx-tests,
it likely needs additional cleanup and testing. I'd like your
thoughs on whether this change makes sense in the first place,
and whether this is generally a reasonable approach - if so I'll
clean up the patch further.

My approach is to allow the authentication server to return a
'Auth-Method: none' header, in which case the proxy will not
attempt to authenticate to the backend but instead wait for
the 'MAIL FROM' from the client.

You'll notice I've added a 'proxy_auth_method'. The reason I didn't
overwrite 'auth_method' is that 'auth_method' is also used to determine
whether to confirm the authentication to the client. Is that acceptable
from a binary compatibility perspective?

Looking forward to hearing your thoughts!

diff -r daf8f5ba23d8 -r 9606e589b953 src/mail/ngx_mail.h
--- a/src/mail/ngx_mail.h Fri Sep 01 20:31:46 2023 +0400
+++ b/src/mail/ngx_mail.h Mon Sep 18 11:01:10 2023 +0200
@@ -212,6 +212,7 @@
unsigned starttls:1;
unsigned esmtp:1;
unsigned auth_method:3;
+ unsigned proxy_auth_method:3;
unsigned auth_wait:1;

ngx_str_t login;
diff -r daf8f5ba23d8 -r 9606e589b953 src/mail/ngx_mail_auth_http_module.c
--- a/src/mail/ngx_mail_auth_http_module.c Fri Sep 01 20:31:46 2023 +0400
+++ b/src/mail/ngx_mail_auth_http_module.c Mon Sep 18 11:01:10 2023 +0200
@@ -677,6 +677,23 @@
continue;
}

+ if (len == sizeof("Auth-Method") - 1
+ && ngx_strncasecmp(ctx->header_name_start,
+ (u_char *) "Auth-Method",
+ sizeof("Auth-Method") - 1)
+ == 0)
+ {
+ int value_len = ctx->header_end - ctx->header_start;
+ if (value_len == sizeof("none") - 1
+ && ngx_strncasecmp(ctx->header_start,
+ (u_char *) "none",
+ sizeof("none") - 1)
+ == 0)
+ {
+ s->proxy_auth_method = NGX_MAIL_AUTH_NONE;
+ }
+ }
+
/* ignore other headers */

continue;
@@ -883,6 +900,7 @@

s->mail_state = 0;
s->auth_method = NGX_MAIL_AUTH_PLAIN;
+ s->proxy_auth_method = NGX_MAIL_AUTH_PLAIN;

c->log->action = "in auth state";

diff -r daf8f5ba23d8 -r 9606e589b953 src/mail/ngx_mail_handler.c
--- a/src/mail/ngx_mail_handler.c Fri Sep 01 20:31:46 2023 +0400
+++ b/src/mail/ngx_mail_handler.c Mon Sep 18 11:01:10 2023 +0200
@@ -714,6 +714,7 @@
"mail auth cram-md5: \"%V\" \"%V\"", &s->login, &s->passwd);

s->auth_method = NGX_MAIL_AUTH_CRAM_MD5;
+ s->proxy_auth_method = NGX_MAIL_AUTH_CRAM_MD5;

return NGX_DONE;
}
@@ -748,6 +749,7 @@
"mail auth external: \"%V\"", &s->login);

s->auth_method = NGX_MAIL_AUTH_EXTERNAL;
+ s->proxy_auth_method = NGX_MAIL_AUTH_EXTERNAL;

return NGX_DONE;
}
diff -r daf8f5ba23d8 -r 9606e589b953 src/mail/ngx_mail_pop3_handler.c
--- a/src/mail/ngx_mail_pop3_handler.c Fri Sep 01 20:31:46 2023 +0400
+++ b/src/mail/ngx_mail_pop3_handler.c Mon Sep 18 11:01:10 2023 +0200
@@ -464,6 +464,7 @@
"pop3 apop: \"%V\" \"%V\"", &s->login, &s->passwd);

s->auth_method = NGX_MAIL_AUTH_APOP;
+ s->proxy_auth_method = NGX_MAIL_AUTH_APOP;

return NGX_DONE;
}
diff -r daf8f5ba23d8 -r 9606e589b953 src/mail/ngx_mail_proxy_module.c
--- a/src/mail/ngx_mail_proxy_module.c Fri Sep 01 20:31:46 2023 +0400
+++ b/src/mail/ngx_mail_proxy_module.c Mon Sep 18 11:01:10 2023 +0200
@@ -605,8 +605,12 @@
if (pcf->xclient) {
s->mail_state = ngx_smtp_helo_xclient;

- } else if (s->auth_method == NGX_MAIL_AUTH_NONE) {
- s->mail_state = ngx_smtp_helo_from;
+ } else if (s->proxy_auth_method == NGX_MAIL_AUTH_NONE) {
+ if (s->smtp_from.len) {
+ s->mail_state = ngx_smtp_helo_from;
+ } else {
+ s->mail_state = ngx_smtp_helo;
+ }

} else if (pcf->smtp_auth) {
s->mail_state = ngx_smtp_helo_auth;
@@ -667,8 +671,12 @@
if (s->smtp_helo.len) {
s->mail_state = ngx_smtp_xclient_helo;

- } else if (s->auth_method == NGX_MAIL_AUTH_NONE) {
- s->mail_state = ngx_smtp_xclient_from;
+ } else if (s->proxy_auth_method == NGX_MAIL_AUTH_NONE) {
+ if (s->smtp_from.len) {
+ s->mail_state = ngx_smtp_xclient_from;
+ } else {
+ s->mail_state = ngx_smtp_xclient_helo;
+ }

} else if (pcf->smtp_auth) {
s->mail_state = ngx_smtp_xclient_auth;
@@ -700,8 +708,12 @@

pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

- if (s->auth_method == NGX_MAIL_AUTH_NONE) {
- s->mail_state = ngx_smtp_helo_from;
+ if (s->proxy_auth_method == NGX_MAIL_AUTH_NONE) {
+ if (s->smtp_from.len) {
+ s->mail_state = ngx_smtp_helo_from;
+ } else {
+ s->mail_state = ngx_smtp_helo;
+ }

} else if (pcf->smtp_auth) {
s->mail_state = ngx_smtp_helo_auth;
diff -r daf8f5ba23d8 -r 9606e589b953 src/mail/ngx_mail_smtp_handler.c
--- a/src/mail/ngx_mail_smtp_handler.c Fri Sep 01 20:31:46 2023 +0400
+++ b/src/mail/ngx_mail_smtp_handler.c Mon Sep 18 11:01:10 2023 +0200
@@ -820,6 +820,7 @@
"smtp rcpt to:\"%V\"", &s->smtp_to);

s->auth_method = NGX_MAIL_AUTH_NONE;
+ s->proxy_auth_method = NGX_MAIL_AUTH_NONE;

return NGX_DONE;
}
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Subject Author Views Posted

[PATCH] Mail: allow auth to the proxy without auth to the backend

Arnout Engelen 150 September 19, 2023 06:30AM

Re: [PATCH] Mail: allow auth to the proxy without auth to the backend

Maxim Dounin 31 September 19, 2023 12:36PM

Re: [PATCH] Mail: allow auth to the proxy without auth to the backend

Arnout Engelen 47 September 19, 2023 01:00PM



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