From 72b224213537d3a42fe15d4fecd3241d2c97f617 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?S=C3=A9bastien=20Helleu?= <flashcode@flashtux.org>
Date: Sun, 12 Oct 2025 16:11:33 +0200
Subject: [PATCH] irc: send SASL username with mechanism EXTERNAL (closes
 #2270)

The SASL username is sent if set, otherwise "+" is still sent.
---
 CHANGELOG.md                             |  1 +
 src/plugins/irc/irc-protocol.c           |  2 +-
 src/plugins/irc/irc-sasl.c               | 29 ++++++++++++++++++++++++
 src/plugins/irc/irc-sasl.h               |  1 +
 tests/unit/plugins/irc/test-irc-sasl.cpp | 15 ++++++++++++
 5 files changed, 47 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 61e3d7eec..33cff60a8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@ SPDX-License-Identifier: GPL-3.0-or-later
 
 - api: add support of date like ISO 8601 but with spaces and lower `t` and `z` in function util_parse_time ([#886](https://github.com/weechat/weechat/issues/886))
 - irc: request and perform SASL authentication when the server advertises SASL support with message "CAP NEW" ([#2277](https://github.com/weechat/weechat/issues/2277))
+- irc: send SASL username with mechanism EXTERNAL ([#2270](https://github.com/weechat/weechat/issues/2270))
 - logger: change default time format to `%@%F %T.%fZ` (UTC) ([#886](https://github.com/weechat/weechat/issues/886))
 - logger: use function util_parse_time to parse date/time in log files ([#886](https://github.com/weechat/weechat/issues/886))
 - xfer: add buffer local variable "server" in DCC CHAT buffers
diff --git a/src/plugins/irc/irc-protocol.c b/src/plugins/irc/irc-protocol.c
index 99d466ec2..fd9c10acc 100644
--- a/src/plugins/irc/irc-protocol.c
+++ b/src/plugins/irc/irc-protocol.c
@@ -591,7 +591,7 @@ IRC_PROTOCOL_CALLBACK(authenticate)
                 sasl_username, sasl_key, &sasl_error);
             break;
         case IRC_SASL_MECHANISM_EXTERNAL:
-            answer = strdup ("+");
+            answer = irc_sasl_mechanism_external (sasl_username);
             break;
     }
     if (answer)
diff --git a/src/plugins/irc/irc-sasl.c b/src/plugins/irc/irc-sasl.c
index f402f4884..1852c2506 100644
--- a/src/plugins/irc/irc-sasl.c
+++ b/src/plugins/irc/irc-sasl.c
@@ -684,3 +684,32 @@ irc_sasl_mechanism_ecdsa_nist256p_challenge (struct t_irc_server *server,
 
     return answer_base64;
 }
+
+/*
+ * Builds answer for SASL authentication, using mechanism "EXTERNAL".
+ *
+ * Note: result must be freed after use.
+ */
+
+char *
+irc_sasl_mechanism_external (const char *sasl_username)
+{
+    char *answer_base64;
+    int length;
+
+    if (!sasl_username || !sasl_username[0])
+        return strdup ("+");
+
+    length = strlen (sasl_username);
+    answer_base64 = malloc ((length * 4) + 1);
+    if (answer_base64)
+    {
+        if (weechat_string_base_encode ("64", sasl_username, length, answer_base64) < 0)
+        {
+            free (answer_base64);
+            answer_base64 = NULL;
+        }
+    }
+
+    return answer_base64;
+}
diff --git a/src/plugins/irc/irc-sasl.h b/src/plugins/irc/irc-sasl.h
index 3f65dd401..d8d40e3b1 100644
--- a/src/plugins/irc/irc-sasl.h
+++ b/src/plugins/irc/irc-sasl.h
@@ -56,5 +56,6 @@ extern char *irc_sasl_mechanism_ecdsa_nist256p_challenge (struct t_irc_server *s
                                                           const char *sasl_username,
                                                           const char *sasl_key,
                                                           char **sasl_error);
+extern char *irc_sasl_mechanism_external (const char *sasl_username);
 
 #endif /* WEECHAT_PLUGIN_IRC_SASL_H */
diff --git a/tests/unit/plugins/irc/test-irc-sasl.cpp b/tests/unit/plugins/irc/test-irc-sasl.cpp
index b87c7cbb4..ca082a9f2 100644
--- a/tests/unit/plugins/irc/test-irc-sasl.cpp
+++ b/tests/unit/plugins/irc/test-irc-sasl.cpp
@@ -114,3 +114,18 @@ TEST(IrcSasl, MechanismEcdsaNist256pChallenge)
 {
     /* TODO: write tests */
 }
+
+/*
+ * Tests functions:
+ *   irc_sasl_mechanism_external
+ */
+
+TEST(IrcSasl, MechanismExternal)
+{
+    char *str;
+
+    WEE_TEST_STR("+", irc_sasl_mechanism_external (NULL));
+    WEE_TEST_STR("+", irc_sasl_mechanism_external (""));
+
+    WEE_TEST_STR("YWxpY2U=", irc_sasl_mechanism_external ("alice"));
+}