SSH lockdown option

README.md

@@ -35,6 +35,17 @@ $ gh-auth add --users=chrishunt --command="tmux attach"
 Adding 2 key(s) to '/Users/chris/.ssh/authorized_keys'
 ```
 
+Allowing someone to SSH to your machine can be a scary thing. Restricting them
+to a single command goes a little way to help secure things, but if you want to
+keep them from forwarding ports and such, try the lockdown option. It prepends
+their key file entry with `no-port-forwarding,no-X11-forwarding,no-agent-forwarding`
+For more information check out the [8th Chapter of the SSH book](http://oreilly.com/catalog/sshtdg/chapter/ch08.html):
+
+```bash
+$ gh-auth add --users=chrishunt --lockdown
+Adding 2 key(s) to '/Users/chris/.ssh/authorized_keys'
+```
+
 That was easy! When we're done working, you can revoke my access with:
 
 ```bash

lib/github/auth/cli.rb

@@ -8,6 +8,7 @@ class CLI < Thor
 
     option :users, type: :array, required: true
     option :command, type: :string
+    option :lockdown, type: :boolean
     desc 'add', 'Add GitHub users to authorized keys'
     long_desc <<-LONGDESC
         `gh-auth add` is used to add one or more GitHub user's public SSH keys
@@ -22,11 +23,16 @@ class CLI < Thor
         the `--command` option.
 
         > $ gh-auth add --users=chrishunt --command="tmux attach"
+
+        You may also "lockdown" shell access, preventing forwarding, by
+        including the `--lockdown` option.
+
+        > $ gh-auth add --users=chrishunt --lockdown
     LONGDESC
     def add
       on_keys_file :write!,
         "Adding #{keys.count} key(s) to '#{keys_file.path}'",
-        { command: options[:command] }
+        { command: options[:command], lockdown: options[:lockdown] }
     end
 
     option :users, type: :array, required: true

lib/github/auth/keys_file.rb

@@ -1,7 +1,7 @@
 module Github::Auth
   # Write and delete keys from the authorized_keys file
   class KeysFile
-    attr_reader :path, :command
+    attr_reader :path, :command, :lockdown
 
     PermissionDeniedError = Class.new StandardError
     FileDoesNotExistError = Class.new StandardError
@@ -10,7 +10,8 @@ class KeysFile
 
     def initialize(options = {})
       @path = File.expand_path(options[:path] || DEFAULT_PATH)
-      @command = options[:command]
+      @command  = options[:command]
+      @lockdown = options.fetch(:lockdown){ false }
     end
 
     def write!(keys)
@@ -20,7 +21,7 @@ def write!(keys)
             unless keys_file_content.empty? || keys_file_content.end_with?("\n")
               keys_file.write "\n"
             end
-            keys_file.write "#{"command=\"#{command}\" " if command}#{key}\n"
+            keys_file.write key_line(key)
           end
         end
       end
@@ -69,5 +70,19 @@ def keys_file_content_without(keys)
         content << "\n" unless content.empty? || content.end_with?("\n")
       end
     end
+
+    def key_line_prefixes
+      prefixes = []
+      prefixes << 'no-port-forwarding,no-X11-forwarding,no-agent-forwarding' if lockdown
+      prefixes << %Q{command="#{command}"} if command
+      prefixes.join(',')
+    end
+
+    def key_line(key)
+      line = []
+      line << key_line_prefixes unless key_line_prefixes.empty?
+      line << "#{key}\n"
+      line.join(' ')
+    end
   end
 end

spec/acceptance/github/auth/cli_spec.rb

@@ -54,6 +54,17 @@ def cli(args = [])
       expect(keys_file.read.strip).to be_empty
     end
 
+    it 'supports ssh "lockdown"' do
+      cli %w(add --users=chrishunt --lockdown)
+
+      expect(keys_file.read).to include 'no-port-forwarding,no-X11-forwarding,no-agent-forwarding'
+
+      keys_file.rewind
+      cli %w(remove --users=chrishunt)
+
+      expect(keys_file.read.strip).to be_empty
+    end
+
     it 'prints version information' do
       output = capture_stdout do
         cli %w(version)

spec/unit/github/auth/keys_file_spec.rb

@@ -92,6 +92,19 @@
       end
     end
 
+    context 'with "lockdown"' do
+      let(:options) {{ path: path, lockdown: true }}
+      let(:keys) {[ Github::Auth::Key.new('chris', 'abc123') ]}
+
+      it_should_behave_like 'a successful key addition'
+
+      it 'prefixes the key with "lockdown" options' do
+        subject.write! keys
+
+        expect(keys_file.read).to include 'no-port-forwarding,no-X11-forwarding,no-agent-forwarding'
+      end
+    end
+
     context 'with existing keys in the keys file' do
       let(:existing_keys) { %w(abc123 def456 ghi789) }
       let(:keys) {[ Github::Auth::Key.new('chris', 'jkl012') ]}