Use an array instead of map

lib/vagrant/util/ssh.rb

@@ -139,7 +139,7 @@ module Vagrant
         end
 
         if ssh_info[:forward_env]
-          command_options += ["-o", "SendEnv=" + ssh_info[:forward_env].keys().join(" ")]
+          command_options += ["-o", "SendEnv=#{ssh_info[:forward_env].join(" ")}"]
         end
 
         # Configurables -- extra_args should always be last due to the way the
@@ -179,8 +179,8 @@ module Vagrant
 
         # Forward configured environment variables.
         if ssh_info[:forward_env]
-          ssh_info[:forward_env].each do |host_var, guest_var|
-            process.environment[guest_var] = ENV[guest_var]
+          ssh_info[:forward_env].each do |key|
+            process.environment[key] = ENV[key]
           end
         end
 

plugins/communicators/ssh/communicator.rb

@@ -328,28 +328,17 @@ module VagrantPlugins
         auth_methods << "publickey" if ssh_info[:private_key_path]
         auth_methods << "password" if ssh_info[:password]
 
-        # Build the environment
-        env_revert = {}
-        send_env_array = nil
-        if ssh_info[:forward_agent]
-          send_env_array = ssh_info[:forward_env].values()
-          ssh_info[:forward_env].each do |host_var, guest_var|
-            env_revert[guest_var] = ENV[guest_var]
-            ENV[guest_var] = ENV[host_var]
-          end
-        end
-
         # Build the options we'll use to initiate the connection via Net::SSH
         common_connect_opts = {
           auth_methods:          auth_methods,
           config:                false,
           forward_agent:         ssh_info[:forward_agent],
+          forward_env:           ssh_info[:forward_env],
           keys:                  ssh_info[:private_key_path],
           keys_only:             true,
           paranoid:              false,
           password:              ssh_info[:password],
           port:                  ssh_info[:port],
-          send_env:              send_env_array,
           timeout:               15,
           user_known_hosts_file: [],
           verbose:               :debug,
@@ -442,11 +431,6 @@ module VagrantPlugins
           # This is raised if a private key type that Net-SSH doesn't support
           # is used. Show a nicer error.
           raise Vagrant::Errors::SSHKeyTypeNotSupported
-        ensure
-          # TODO: will this leak?
-          env_revert.each do |guest_var, guest_value|
-            ENV[guest_var] = guest_value
-          end
         end
 
         @connection          = connection

website/docs/source/v2/vagrantfile/ssh_settings.html.md

@@ -67,8 +67,13 @@ is enabled. Defaults to false.
 
 <hr>
 
-`config.ssh.forward_env` - A hash of host environment variable names to guest
-environment variable names.
+`config.ssh.forward_env` - An array of host environment variables to forward to
+the guest. If you are familiar with OpenSSH, this corresponds to the `SendEnv`
+paramter.
+
+```ruby
+config.ssh.forward_env = ["CUSTOM_VAR"]
+```
 
 <hr>