Added option to disable building AES-GCM support (see #2024 and #2054)

configure.ac

@@ -126,6 +126,12 @@ AC_ARG_ENABLE([libsrtp2],
               [],
               [enable_libsrtp2=maybe])
 
+AC_ARG_ENABLE([aes-gcm],
+              [AS_HELP_STRING([--disable-aes-gcm],
+                              [Disable AES-GCM support in libsrtp(2)])],
+              [],
+              [AC_DEFINE(HAVE_SRTP_AESGCM)])
+
 AC_ARG_ENABLE([dtls-settimeout],
               [AS_HELP_STRING([--enable-dtls-settimeout],
                               [Use DTLSv1_set_initial_timeout_duration (only available in recent BoringSSL versions)])],
@@ -391,7 +397,6 @@ AS_IF([test "x$enable_libsrtp2" != "xno"],
                          [libsrtp2],
                          [
                           AC_DEFINE(HAVE_SRTP_2)
-                          AC_DEFINE(HAVE_SRTP_AESGCM)
                           enable_libsrtp2=yes
                           AM_CONDITIONAL([ENABLE_LIBSRTP_2], true)
                          ],
@@ -404,10 +409,7 @@ AM_COND_IF([ENABLE_LIBSRTP_2],
            [],
            [PKG_CHECK_MODULES([LIBSRTP],
                               [libsrtp >= 1.5.0],
-                              [
-                               AC_DEFINE(HAVE_SRTP_AESGCM)
-                               enable_libsrtp2=no
-                              ],
+                              [enable_libsrtp2=no],
                               [AC_MSG_ERROR([libsrtp and libsrtp2 not found. See README.md for installation instructions])
                               ])
            ])

mainpage.dox

@@ -3745,6 +3745,8 @@ ldd janus | grep asan
  * -# <a href="#writeplugin">I want to write my own plugin, where do I start?</a>\n
  * -# <a href="#ulimit">I'm using the VideoRoom plugin and, when several users are handled, I get
  *    a "Too many open files" errors and Janus crashes</a>\n
+ * -# <a href="#aesgcm">I get an undefined reference to <code>srtp_crypto_policy_set_aes_gcm_256_16_auth</code>
+ *    when building Janus</a>\n
  * -# <a href="#https">When I enable the HTTPS web server in Janus, the CPU goes crazy</a>\n
  * -# <a href="#turn">I enabled TURN in the Janus configuration, but my clients behind a firewall can't connect</a>\n
  * -# <a href="#benchmark">Is there any benchmark on Janus performances?</a>\n
@@ -4118,6 +4120,17 @@ ldd janus | grep asan
  *    this refer to the guide provided by the MongoDB developers:
  *    http://docs.mongodb.org/manual/reference/ulimit/ \n\n
  *    .
+ * \anchor aesgcm
+ * -# <b>I get an undefined reference to <code>srtp_crypto_policy_set_aes_gcm_256_16_auth</code>
+ *    when building Janus</b>\n
+ *    .
+ *    As explained in the README, you have to build libsrtp or libsrtp2 with
+ *    the <code>--enable-openssl</code> or <code>--enable-nss</code> flags,
+ *    since they're needed to support AES-GCM in our SRTP streams. If you
+ *    don't want AES-GCM support, pass the <code>--disable-aes-gcm</code>
+ *    option when configuring Janus instead: remember to do a
+ *    <code>make clean</code> before recompiling Janus after the change. \n\n
+ *    .
  * \anchor https
  * -# <b>When I enable the HTTPS web server in Janus, the CPU goes crazy</b>\n
  *    .