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.

10 files changed, 110 insertions, 15 deletions

diff --git a/src/mail/ngx_mail.h b/src/mail/ngx_mail.h
index c30af35c9..600250820 100644
--- 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(ngx_mail_session_t *s,
 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
index a94434a2f..6b57358b4 100644
--- 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_method[] = {
     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
index 901bb8f15..9d4ef561b 100644
--- 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_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_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
index 57e2fb77d..1c5445785 100644
--- 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 *rev)
         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_session_t *s, ngx_connection_t *c)
         }
 
         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
index d281070fb..1f187fdee 100644
--- 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_auth_methods[] = {
     { 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_methods_names[] = {
     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 *cf, void *parent, void *child)
     }
 
     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 *cf, void *parent, void *child)
     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
index b158f5a0f..2c2cdffa1 100644
--- 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 *s, ngx_connection_t *c)
 
     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 *) "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
index 51bc257a5..a2d565804 100644
--- 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 *rev)
         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, ngx_connection_t *c)
         }
 
         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
index efd298fcd..bd60e0a67 100644
--- 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_auth_methods[] = {
     { 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_methods_names[] = {
     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 *cf, void *parent, void *child)
     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 *cf, void *parent, void *child)
     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 *cf, void *parent, void *child)
            + 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 *cf, void *parent, void *child)
                    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
index 81cc75f24..47756c311 100644
--- 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 *rev)
         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, ngx_connection_t *c)
         }
 
         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
index d5bb51cc2..f03bd907e 100644
--- 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_auth_methods[] = {
     { 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_methods_names[] = {
     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 *cf, void *parent, void *child)
     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 *cf, void *parent, void *child)
         *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) {