sasl: Implement SASL authorisation identity via CURLOPT_SASL_AUTHZID

Added the ability for the calling program to specify the authorisation
identity (authzid), the identity to act as, in addition to the
authentication identity (authcid) and password when using SASL PLAIN
authentication.

Fixed #3653
Closes #3790

4 files changed, 68 insertions, 0 deletions

diff --git a/docs/libcurl/curl_easy_setopt.3 b/docs/libcurl/curl_easy_setopt.3
index 1f18a3494..a523364cd 100644
--- a/docs/libcurl/curl_easy_setopt.3
+++ b/docs/libcurl/curl_easy_setopt.3
@@ -256,6 +256,8 @@ TLS authentication methods. See \fICURLOPT_TLSAUTH_TYPE(3)\fP
 Proxy TLS authentication methods. See \fICURLOPT_PROXY_TLSAUTH_TYPE(3)\fP
 .IP CURLOPT_PROXYAUTH
 HTTP proxy authentication methods. See \fICURLOPT_PROXYAUTH(3)\fP
+.IP CURLOPT_SASL_AUTHZID
+SASL authorisation identity (identity to act as). See \fICURLOPT_SASL_AUTHZID(3)\fP 
 .IP CURLOPT_SASL_IR
 Enable SASL initial response. See \fICURLOPT_SASL_IR(3)\fP
 .IP CURLOPT_XOAUTH2_BEARER
diff --git a/docs/libcurl/opts/CURLOPT_SASL_AUTHZID.3 b/docs/libcurl/opts/CURLOPT_SASL_AUTHZID.3
new file mode 100644
index 000000000..79b360b5e
--- /dev/null
+++ b/docs/libcurl/opts/CURLOPT_SASL_AUTHZID.3
@@ -0,0 +1,64 @@
+.\" **************************************************************************
+.\" *                                  _   _ ____  _
+.\" *  Project                     ___| | | |  _ \| |
+.\" *                             / __| | | | |_) | |
+.\" *                            | (__| |_| |  _ <| |___
+.\" *                             \___|\___/|_| \_\_____|
+.\" *
+.\" * Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" *
+.\" * This software is licensed as described in the file COPYING, which
+.\" * you should have received as part of this distribution. The terms
+.\" * are also available at https://curl.haxx.se/docs/copyright.html.
+.\" *
+.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+.\" * copies of the Software, and permit persons to whom the Software is
+.\" * furnished to do so, under the terms of the COPYING file.
+.\" *
+.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+.\" * KIND, either express or implied.
+.\" *
+.\" **************************************************************************
+.\"
+.TH CURLOPT_SASL_AUTHZID 3 "17 July 2019" "libcurl 7.66.0" "curl_easy_setopt options"
+.SH NAME
+CURLOPT_SASL_AUTHZID \- authorisation identity (identity to act as)
+.SH SYNOPSIS
+#include <curl/curl.h>
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SASL_AUTHZID, char *authzid);
+.SH DESCRIPTION
+Pass a char * as parameter, which should be pointing to the zero terminated
+authorisation identity (authzid) for the transfer. Only applicable to the PLAIN
+SASL authentication mechanism where it is optional.
+
+When not specified only the authentication identity (authcid) as specified by
+the username will be sent to the server, along with the password. The server
+will derive a authzid from the authcid when not provided, which it will then
+uses internally.
+
+When the authzid is specified, the use of which is server dependent, it can be
+used to access another user's inbox, that the user has been granted access to,
+or a shared mailbox for example.
+.SH DEFAULT
+blank
+.SH PROTOCOLS
+IMAP, POP3 and SMTP
+.SH EXAMPLE
+.nf
+CURL *curl = curl_easy_init();
+if(curl) {
+  curl_easy_setopt(curl, CURLOPT_URL, "imap://example.com/");
+  curl_easy_setopt(curl, CURLOPT_USERNAME, "Kurt");
+  curl_easy_setopt(curl, CURLOPT_PASSWORD, "xipj3plmq");
+  curl_easy_setopt(curl, CURLOPT_SASL_AUTHZID, "Ursel");
+  ret = curl_easy_perform(curl);
+  curl_easy_cleanup(curl);
+}
+.fi
+.SH AVAILABILITY
+Added in 7.66.0
+.SH RETURN VALUE
+Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
+.SH "SEE ALSO"
+.BR CURLOPT_USERNAME "(3), " CURLOPT_PASSWORD "(3), ".BR CURLOPT_USERPWD "(3)"
diff --git a/docs/libcurl/opts/Makefile.inc b/docs/libcurl/opts/Makefile.inc
index c8e15a5ed..9a1016c3f 100644
--- a/docs/libcurl/opts/Makefile.inc
+++ b/docs/libcurl/opts/Makefile.inc
@@ -272,6 +272,7 @@ man_MANS =                                      \
   CURLOPT_RTSP_SESSION_ID.3                     \
   CURLOPT_RTSP_STREAM_URI.3                     \
   CURLOPT_RTSP_TRANSPORT.3                      \
+  CURLOPT_SASL_AUTHZID.3                        \
   CURLOPT_SASL_IR.3                             \
   CURLOPT_SEEKDATA.3                            \
   CURLOPT_SEEKFUNCTION.3                        \
diff --git a/docs/libcurl/symbols-in-versions b/docs/libcurl/symbols-in-versions
index 715badf97..addbaf905 100644
--- a/docs/libcurl/symbols-in-versions
+++ b/docs/libcurl/symbols-in-versions
@@ -553,6 +553,7 @@ CURLOPT_RTSP_SERVER_CSEQ        7.20.0
 CURLOPT_RTSP_SESSION_ID         7.20.0
 CURLOPT_RTSP_STREAM_URI         7.20.0
 CURLOPT_RTSP_TRANSPORT          7.20.0
+CURLOPT_SASL_AUTHZID            7.66.0
 CURLOPT_SASL_IR                 7.31.0
 CURLOPT_SEEKDATA                7.18.0
 CURLOPT_SEEKFUNCTION            7.18.0