ssl: Backport cert_auth exclusion option to pre TLS-1.3

lib/ssl/src/ssl.erl

@@ -1776,6 +1776,11 @@ Certificate related options for a server.
   certificate request message that is sent when the option `verify` is set to
   `verify_peer`. Defaults to `true`.
 
+  If set to `false` for older TLS versions its corresponding certificate authorities
+  defenition in its certificate request will be set to the empty list instead of
+  including the appropriate certificate authorities. This has the same affect
+  as excluding the TLS-1.3 extension.
+
   A reason to exclude the extension would be if the server wants to communicate
   with clients incapable of sending complete certificate chains that adhere to the
   extension, but the server still has the capability to recreate a chain that it
@@ -4080,8 +4085,12 @@ opt_cacerts(UserOpts, #{verify := Verify, log_level := LogLevel, versions := Ver
                         [{verify, verify_peer}, {cacerts, undefined}]),
 
     {Where2, CA} = get_opt_bool(certificate_authorities, Role =:= server, UserOpts, Opts),
-    assert_version_dep(Where2 =:= new, certificate_authorities, Versions, ['tlsv1.3']),
-
+    case Role of
+        server ->
+            assert_version_dep(Where2 =:= new, certificate_authorities, Versions, ['tlsv1.3', 'tlsv1.2', 'tlsv1.1', 'tlsv1']);
+        client ->
+            assert_version_dep(Where2 =:= new, certificate_authorities, Versions, ['tlsv1.3'])
+    end,
     Opts1 = set_opt_new(new, cacertfile, <<>>, CaCertFile, Opts),
     Opts2 = set_opt_new(Where2, certificate_authorities, Role =:= server, CA, Opts1),
     Opts2#{cacerts => CaCerts}.

lib/ssl/src/ssl_handshake.erl

@@ -63,7 +63,7 @@
          server_hello_done/0,
 	 certificate/4,
          client_certificate_verify/6,
-         certificate_request/4,
+         certificate_request/5,
          key_exchange/3,
 	 finished/5,
          next_protocol/1,
@@ -219,19 +219,25 @@ client_certificate_verify([OwnCert|_], MasterSecret, Version,
 
 %%--------------------------------------------------------------------
 -spec certificate_request(ssl_manager:db_handle(),
-			  ssl_manager:certdb_ref(),  #hash_sign_algos{}, ssl_record:ssl_version()) ->
-				 #certificate_request{}.
+			  ssl_manager:certdb_ref(),  #hash_sign_algos{}, 
+                          ssl_record:ssl_version(), boolean()) ->
+          #certificate_request{}.
 %%
 %% Description: Creates a certificate_request message, called by the server.
 %%--------------------------------------------------------------------
-certificate_request(CertDbHandle, CertDbRef, HashSigns, Version) ->
+certificate_request(CertDbHandle, CertDbRef, HashSigns, Version, IncludeCertAuths) ->
     Types = certificate_types(Version),
-    Authorities = certificate_authorities(CertDbHandle, CertDbRef),
+    Authorities = case IncludeCertAuths of
+                      true ->
+                          certificate_authorities(CertDbHandle, CertDbRef);
+                      false ->
+                          []
+                  end,
     #certificate_request{
-		    certificate_types = Types,
-		    hashsign_algorithms = HashSigns,
-		    certificate_authorities = Authorities
-		   }.
+       certificate_types = Types,
+       hashsign_algorithms = HashSigns,
+       certificate_authorities = Authorities
+      }.
 %%--------------------------------------------------------------------
 -spec key_exchange(client | server, ssl_record:ssl_version(),
 		   {premaster_secret, binary(), public_key_info()} |

lib/ssl/src/tls_dtls_server_connection.erl

@@ -660,8 +660,9 @@ request_client_cert(#state{static_env = #static_env{cert_db = CertDbHandle,
     TLSVersion =  ssl:tls_version(Version),
     HashSigns = ssl_handshake:available_signature_algs(SupportedHashSigns,
 						       TLSVersion),
+    IncludeCertAuths = maps:get(certificate_authorities, Opts, true),
     Msg = ssl_handshake:certificate_request(CertDbHandle, CertDbRef,
-					    HashSigns, TLSVersion),
+					    HashSigns, TLSVersion, IncludeCertAuths),
     #state{handshake_env = HsEnv0} = State = Connection:queue_handshake(Msg, State0),
     HsEnv = HsEnv0#handshake_env{client_certificate_status = requested},
     State#state{handshake_env = HsEnv};

lib/ssl/test/ssl_api_SUITE.erl

@@ -2772,6 +2772,7 @@ options_certificate_authorities(_Config) ->
     ?OK(#{certificate_authorities := true}, [{certificate_authorities, true}], client),
     ?OK(#{}, [{certificate_authorities, false}], client, [certificate_authorities]),
     ?OK(#{certificate_authorities := false}, [{certificate_authorities, false}], server),
+    ?OK(#{certificate_authorities := false}, [{certificate_authorities, false}, {versions, ['tlsv1.2']}], server),
     ?OK(#{}, [{certificate_authorities, true}], server, [certificate_authorities]),
 
     %% Errors

lib/ssl/test/ssl_cert_SUITE.erl

@@ -131,6 +131,8 @@
          signature_algorithms_bad_curve_secp521r1/1,
          server_certificate_authorities_disabled/0,
          server_certificate_authorities_disabled/1,
+         legacy_server_certificate_authorities_disabled/0,
+         legacy_server_certificate_authorities_disabled/1,
          cert_auth_in_first_ca/0,
          cert_auth_in_first_ca/1
          ]).
@@ -207,7 +209,8 @@ tls_1_3_tests() ->
 
 pre_tls_1_3_rsa_tests() ->
     [
-     key_auth_ext_sign_only
+     key_auth_ext_sign_only,
+     legacy_server_certificate_authorities_disabled
     ].
 
 rsa_tests() ->
@@ -1405,6 +1408,19 @@ server_certificate_authorities_disabled(Config) ->
     ssl_test_lib:basic_alert(ClientOpts, ServerOpts, Config, certificate_required),
     ssl_test_lib:basic_test(ClientOpts, [{certificate_authorities, false} | ServerOpts], Config).
 
+%%--------------------------------------------------------------------
+legacy_server_certificate_authorities_disabled() ->
+     [{doc,"Test that code pre TLS-1.3 can send an empty list for certificate authorities in the certificate request"
+       "will be run and not fail, black box verification is not possible without strict legacy client, but code coverage will show that right thing happens"}].
+
+legacy_server_certificate_authorities_disabled(Config) ->
+    Version = proplists:get_value(version,Config),
+    ClientOpts = ssl_test_lib:ssl_options(client_cert_opts, Config),
+    ServerOpts = ssl_test_lib:ssl_options(server_cert_opts, Config),
+    ssl_test_lib:basic_test([{versions, [Version]} | ClientOpts], [{versions, [Version]}, {verify, verify_peer},
+                                                                  {fail_if_no_peer_cert, true},
+                                                                  {certificate_authorities, false} | ServerOpts], Config).
+
 %%--------------------------------------------------------------------
 %% Internal functions  -----------------------------------------------
 %%--------------------------------------------------------------------