# HG changeset patch
# User Rob N ★ <robn@fastmail.com>
# Date 1475910300 -39600
# Node ID bcb107bb89cd9c1f20e31f6f56c2171b2b3e7721
# Parent  73b451d304c0cf6502eb5d93404aded1db59ec40
Mail: support SASL EXTERNAL (RFC 4422).

This is needed to allow TLS client certificate auth to work. With
ssl_verify_client configured, the auth daemon can choose to allow the
connection to proceed based on the certificate data.

This has been tested with Thunderbird for IMAP only. I've not yet found a
client that will do client certificate auth for POP3 or SMTP, and the method is
not really documented anywhere that I can find. That said, its simple enough
that the way I've done is probably right.

diff --git a/src/mail/ngx_mail.h b/src/mail/ngx_mail.h
--- a/src/mail/ngx_mail.h
+++ b/src/mail/ngx_mail.h
@@ -132,7 +132,8 @@ typedef enum {
     ngx_pop3_auth_login_username,
     ngx_pop3_auth_login_password,
     ngx_pop3_auth_plain,
-    ngx_pop3_auth_cram_md5
+    ngx_pop3_auth_cram_md5,
+    ngx_pop3_auth_external
 } ngx_pop3_state_e;
 
 
@@ -142,6 +143,7 @@ typedef enum {
     ngx_imap_auth_login_password,
     ngx_imap_auth_plain,
     ngx_imap_auth_cram_md5,
+    ngx_imap_auth_external,
     ngx_imap_login,
     ngx_imap_user,
     ngx_imap_passwd
@@ -154,6 +156,7 @@ typedef enum {
     ngx_smtp_auth_login_password,
     ngx_smtp_auth_plain,
     ngx_smtp_auth_cram_md5,
+    ngx_smtp_auth_external,
     ngx_smtp_helo,
     ngx_smtp_helo_xclient,
     ngx_smtp_helo_from,
@@ -285,14 +288,16 @@ typedef struct {
 #define NGX_MAIL_AUTH_LOGIN_USERNAME    2
 #define NGX_MAIL_AUTH_APOP              3
 #define NGX_MAIL_AUTH_CRAM_MD5          4
-#define NGX_MAIL_AUTH_NONE              5
+#define NGX_MAIL_AUTH_EXTERNAL          5
+#define NGX_MAIL_AUTH_NONE              6
 
 
 #define NGX_MAIL_AUTH_PLAIN_ENABLED     0x0002
 #define NGX_MAIL_AUTH_LOGIN_ENABLED     0x0004
 #define NGX_MAIL_AUTH_APOP_ENABLED      0x0008
 #define NGX_MAIL_AUTH_CRAM_MD5_ENABLED  0x0010
-#define NGX_MAIL_AUTH_NONE_ENABLED      0x0020
+#define NGX_MAIL_AUTH_EXTERNAL_ENABLED  0x0020
+#define NGX_MAIL_AUTH_NONE_ENABLED      0x0040
 
 
 #define NGX_MAIL_PARSE_INVALID_COMMAND  20
@@ -377,6 +382,8 @@ ngx_int_t ngx_mail_auth_login_password(n
 ngx_int_t ngx_mail_auth_cram_md5_salt(ngx_mail_session_t *s,
     ngx_connection_t *c, char *prefix, size_t len);
 ngx_int_t ngx_mail_auth_cram_md5(ngx_mail_session_t *s, ngx_connection_t *c);
+ngx_int_t ngx_mail_auth_external(ngx_mail_session_t *s, ngx_connection_t *c,
+    ngx_uint_t n);
 ngx_int_t ngx_mail_auth_parse(ngx_mail_session_t *s, ngx_connection_t *c);
 
 void ngx_mail_send(ngx_event_t *wev);
diff --git a/src/mail/ngx_mail_auth_http_module.c b/src/mail/ngx_mail_auth_http_module.c
--- a/src/mail/ngx_mail_auth_http_module.c
+++ b/src/mail/ngx_mail_auth_http_module.c
@@ -151,6 +151,7 @@ static ngx_str_t   ngx_mail_auth_http_me
     ngx_string("plain"),
     ngx_string("apop"),
     ngx_string("cram-md5"),
+    ngx_string("external"),
     ngx_string("none")
 };
 
diff --git a/src/mail/ngx_mail_handler.c b/src/mail/ngx_mail_handler.c
--- a/src/mail/ngx_mail_handler.c
+++ b/src/mail/ngx_mail_handler.c
@@ -612,6 +612,40 @@ ngx_mail_auth_cram_md5(ngx_mail_session_
 }
 
 
+ngx_int_t
+ngx_mail_auth_external(ngx_mail_session_t *s, ngx_connection_t *c,
+    ngx_uint_t n)
+{
+    ngx_str_t  *arg, external;
+
+    arg = s->args.elts;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_MAIL, c->log, 0,
+                   "mail auth external: \"%V\"", &arg[n]);
+
+    external.data = ngx_pnalloc(c->pool, ngx_base64_decoded_length(arg[n].len));
+    if (external.data == NULL) {
+        return NGX_ERROR;
+    }
+
+    if (ngx_decode_base64(&external, &arg[n]) != NGX_OK) {
+        ngx_log_error(NGX_LOG_INFO, c->log, 0,
+            "client sent invalid base64 encoding in AUTH EXTERNAL command");
+        return NGX_MAIL_PARSE_INVALID_COMMAND;
+    }
+
+    s->login.len = external.len;
+    s->login.data = external.data;
+
+    ngx_log_debug1(NGX_LOG_DEBUG_MAIL, c->log, 0,
+                   "mail auth external: \"%V\"", &s->login);
+
+    s->auth_method = NGX_MAIL_AUTH_EXTERNAL;
+
+    return NGX_DONE;
+}
+
+
 void
 ngx_mail_send(ngx_event_t *wev)
 {
diff --git a/src/mail/ngx_mail_imap_handler.c b/src/mail/ngx_mail_imap_handler.c
--- a/src/mail/ngx_mail_imap_handler.c
+++ b/src/mail/ngx_mail_imap_handler.c
@@ -222,6 +222,10 @@ ngx_mail_imap_auth_state(ngx_event_t *re
         case ngx_imap_auth_cram_md5:
             rc = ngx_mail_auth_cram_md5(s, c);
             break;
+
+        case ngx_imap_auth_external:
+            rc = ngx_mail_auth_external(s, c, 0);
+            break;
         }
 
     } else if (rc == NGX_IMAP_NEXT) {
@@ -399,6 +403,13 @@ ngx_mail_imap_authenticate(ngx_mail_sess
         }
 
         return NGX_ERROR;
+
+    case NGX_MAIL_AUTH_EXTERNAL:
+
+        ngx_str_set(&s->out, imap_username);
+        s->mail_state = ngx_imap_auth_external;
+
+        return NGX_OK;
     }
 
     return rc;
diff --git a/src/mail/ngx_mail_imap_module.c b/src/mail/ngx_mail_imap_module.c
--- a/src/mail/ngx_mail_imap_module.c
+++ b/src/mail/ngx_mail_imap_module.c
@@ -29,6 +29,7 @@ static ngx_conf_bitmask_t  ngx_mail_imap
     { ngx_string("plain"), NGX_MAIL_AUTH_PLAIN_ENABLED },
     { ngx_string("login"), NGX_MAIL_AUTH_LOGIN_ENABLED },
     { ngx_string("cram-md5"), NGX_MAIL_AUTH_CRAM_MD5_ENABLED },
+    { ngx_string("external"), NGX_MAIL_AUTH_EXTERNAL_ENABLED },
     { ngx_null_string, 0 }
 };
 
@@ -38,6 +39,7 @@ static ngx_str_t  ngx_mail_imap_auth_met
     ngx_string("AUTH=LOGIN"),
     ngx_null_string,  /* APOP */
     ngx_string("AUTH=CRAM-MD5"),
+    ngx_string("AUTH=EXTERNAL"),
     ngx_null_string   /* NONE */
 };
 
@@ -179,7 +181,7 @@ ngx_mail_imap_merge_srv_conf(ngx_conf_t 
     }
 
     for (m = NGX_MAIL_AUTH_PLAIN_ENABLED, i = 0;
-         m <= NGX_MAIL_AUTH_CRAM_MD5_ENABLED;
+         m <= NGX_MAIL_AUTH_EXTERNAL_ENABLED;
          m <<= 1, i++)
     {
         if (m & conf->auth_methods) {
@@ -205,7 +207,7 @@ ngx_mail_imap_merge_srv_conf(ngx_conf_t 
     auth = p;
 
     for (m = NGX_MAIL_AUTH_PLAIN_ENABLED, i = 0;
-         m <= NGX_MAIL_AUTH_CRAM_MD5_ENABLED;
+         m <= NGX_MAIL_AUTH_EXTERNAL_ENABLED;
          m <<= 1, i++)
     {
         if (m & conf->auth_methods) {
diff --git a/src/mail/ngx_mail_parse.c b/src/mail/ngx_mail_parse.c
--- a/src/mail/ngx_mail_parse.c
+++ b/src/mail/ngx_mail_parse.c
@@ -905,13 +905,27 @@ ngx_mail_auth_parse(ngx_mail_session_t *
 
     if (arg[0].len == 8) {
 
-        if (s->args.nelts != 1) {
-            return NGX_MAIL_PARSE_INVALID_COMMAND;
+        if (ngx_strncasecmp(arg[0].data, (u_char *) "CRAM-MD5", 8) == 0) {
+
+            if (s->args.nelts != 1) {
+                return NGX_MAIL_PARSE_INVALID_COMMAND;
+            }
+
+            return NGX_MAIL_AUTH_CRAM_MD5;
         }
 
-        if (ngx_strncasecmp(arg[0].data, (u_char *) "CRAM-MD5", 8) == 0) {
-            return NGX_MAIL_AUTH_CRAM_MD5;
+        if (ngx_strncasecmp(arg[0].data, (u_char *) "EXTERNAL", 8) == 0) {
+
+            if (s->args.nelts == 1) {
+                return NGX_MAIL_AUTH_EXTERNAL;
+            }
+
+            if (s->args.nelts == 2) {
+                return ngx_mail_auth_external(s, c, 1);
+            }
         }
+
+        return NGX_MAIL_PARSE_INVALID_COMMAND;
     }
 
     return NGX_MAIL_PARSE_INVALID_COMMAND;
diff --git a/src/mail/ngx_mail_pop3_handler.c b/src/mail/ngx_mail_pop3_handler.c
--- a/src/mail/ngx_mail_pop3_handler.c
+++ b/src/mail/ngx_mail_pop3_handler.c
@@ -240,6 +240,10 @@ ngx_mail_pop3_auth_state(ngx_event_t *re
         case ngx_pop3_auth_cram_md5:
             rc = ngx_mail_auth_cram_md5(s, c);
             break;
+
+        case ngx_pop3_auth_external:
+            rc = ngx_mail_auth_external(s, c, 0);
+            break;
         }
     }
 
@@ -494,6 +498,13 @@ ngx_mail_pop3_auth(ngx_mail_session_t *s
         }
 
         return NGX_ERROR;
+
+    case NGX_MAIL_AUTH_EXTERNAL:
+
+        ngx_str_set(&s->out, pop3_username);
+        s->mail_state = ngx_pop3_auth_external;
+
+        return NGX_OK;
     }
 
     return rc;
diff --git a/src/mail/ngx_mail_pop3_module.c b/src/mail/ngx_mail_pop3_module.c
--- a/src/mail/ngx_mail_pop3_module.c
+++ b/src/mail/ngx_mail_pop3_module.c
@@ -29,6 +29,7 @@ static ngx_conf_bitmask_t  ngx_mail_pop3
     { ngx_string("plain"), NGX_MAIL_AUTH_PLAIN_ENABLED },
     { ngx_string("apop"), NGX_MAIL_AUTH_APOP_ENABLED },
     { ngx_string("cram-md5"), NGX_MAIL_AUTH_CRAM_MD5_ENABLED },
+    { ngx_string("external"), NGX_MAIL_AUTH_EXTERNAL_ENABLED },
     { ngx_null_string, 0 }
 };
 
@@ -38,6 +39,7 @@ static ngx_str_t  ngx_mail_pop3_auth_met
     ngx_string("LOGIN"),
     ngx_null_string,  /* APOP */
     ngx_string("CRAM-MD5"),
+    ngx_string("EXTERNAL"),
     ngx_null_string   /* NONE */
 };
 
@@ -180,7 +182,7 @@ ngx_mail_pop3_merge_srv_conf(ngx_conf_t 
     size += sizeof("SASL") - 1 + sizeof(CRLF) - 1;
 
     for (m = NGX_MAIL_AUTH_PLAIN_ENABLED, i = 0;
-         m <= NGX_MAIL_AUTH_CRAM_MD5_ENABLED;
+         m <= NGX_MAIL_AUTH_EXTERNAL_ENABLED;
          m <<= 1, i++)
     {
         if (m & conf->auth_methods) {
@@ -207,7 +209,7 @@ ngx_mail_pop3_merge_srv_conf(ngx_conf_t 
     p = ngx_cpymem(p, "SASL", sizeof("SASL") - 1);
 
     for (m = NGX_MAIL_AUTH_PLAIN_ENABLED, i = 0;
-         m <= NGX_MAIL_AUTH_CRAM_MD5_ENABLED;
+         m <= NGX_MAIL_AUTH_EXTERNAL_ENABLED;
          m <<= 1, i++)
     {
         if (m & conf->auth_methods) {
@@ -243,7 +245,7 @@ ngx_mail_pop3_merge_srv_conf(ngx_conf_t 
            + sizeof("." CRLF) - 1;
 
     for (m = NGX_MAIL_AUTH_PLAIN_ENABLED, i = 0;
-         m <= NGX_MAIL_AUTH_CRAM_MD5_ENABLED;
+         m <= NGX_MAIL_AUTH_EXTERNAL_ENABLED;
          m <<= 1, i++)
     {
         if (m & conf->auth_methods) {
@@ -264,7 +266,7 @@ ngx_mail_pop3_merge_srv_conf(ngx_conf_t 
                    sizeof("+OK methods supported:" CRLF) - 1);
 
     for (m = NGX_MAIL_AUTH_PLAIN_ENABLED, i = 0;
-         m <= NGX_MAIL_AUTH_CRAM_MD5_ENABLED;
+         m <= NGX_MAIL_AUTH_EXTERNAL_ENABLED;
          m <<= 1, i++)
     {
         if (m & conf->auth_methods) {
diff --git a/src/mail/ngx_mail_smtp_handler.c b/src/mail/ngx_mail_smtp_handler.c
--- a/src/mail/ngx_mail_smtp_handler.c
+++ b/src/mail/ngx_mail_smtp_handler.c
@@ -485,6 +485,10 @@ ngx_mail_smtp_auth_state(ngx_event_t *re
         case ngx_smtp_auth_cram_md5:
             rc = ngx_mail_auth_cram_md5(s, c);
             break;
+
+        case ngx_smtp_auth_external:
+            rc = ngx_mail_auth_external(s, c, 0);
+            break;
         }
     }
 
@@ -652,6 +656,13 @@ ngx_mail_smtp_auth(ngx_mail_session_t *s
         }
 
         return NGX_ERROR;
+
+    case NGX_MAIL_AUTH_EXTERNAL:
+
+        ngx_str_set(&s->out, smtp_username);
+        s->mail_state = ngx_smtp_auth_external;
+
+        return NGX_OK;
     }
 
     return rc;
diff --git a/src/mail/ngx_mail_smtp_module.c b/src/mail/ngx_mail_smtp_module.c
--- a/src/mail/ngx_mail_smtp_module.c
+++ b/src/mail/ngx_mail_smtp_module.c
@@ -21,6 +21,7 @@ static ngx_conf_bitmask_t  ngx_mail_smtp
     { ngx_string("plain"), NGX_MAIL_AUTH_PLAIN_ENABLED },
     { ngx_string("login"), NGX_MAIL_AUTH_LOGIN_ENABLED },
     { ngx_string("cram-md5"), NGX_MAIL_AUTH_CRAM_MD5_ENABLED },
+    { ngx_string("external"), NGX_MAIL_AUTH_EXTERNAL_ENABLED },
     { ngx_string("none"), NGX_MAIL_AUTH_NONE_ENABLED },
     { ngx_null_string, 0 }
 };
@@ -31,6 +32,7 @@ static ngx_str_t  ngx_mail_smtp_auth_met
     ngx_string("LOGIN"),
     ngx_null_string,  /* APOP */
     ngx_string("CRAM-MD5"),
+    ngx_string("EXTERNAL"),
     ngx_null_string   /* NONE */
 };
 
@@ -207,7 +209,7 @@ ngx_mail_smtp_merge_srv_conf(ngx_conf_t 
     auth_enabled = 0;
 
     for (m = NGX_MAIL_AUTH_PLAIN_ENABLED, i = 0;
-         m <= NGX_MAIL_AUTH_CRAM_MD5_ENABLED;
+         m <= NGX_MAIL_AUTH_EXTERNAL_ENABLED;
          m <<= 1, i++)
     {
         if (m & conf->auth_methods) {
@@ -250,7 +252,7 @@ ngx_mail_smtp_merge_srv_conf(ngx_conf_t 
         *p++ = 'A'; *p++ = 'U'; *p++ = 'T'; *p++ = 'H';
 
         for (m = NGX_MAIL_AUTH_PLAIN_ENABLED, i = 0;
-             m <= NGX_MAIL_AUTH_CRAM_MD5_ENABLED;
+             m <= NGX_MAIL_AUTH_EXTERNAL_ENABLED;
              m <<= 1, i++)
         {
             if (m & conf->auth_methods) {