External auth support and vault host selection

Use external program lite Kerberos authenticator for example to get vault token and use DNS to get FQDN for proper
hostname for the domain. This is used not to put the token into the hiera.yaml

lib/hiera/backend/vault_backend.rb

@@ -1,12 +1,48 @@
 # Vault backend for Hiera
 class Hiera
+  # Due to the authentication information might be not avaliable
+  # on the moment when the Puppet is runed for the first time, 
+  # addig the variable that indicates if the actual authentication
+  # already happened.
+  # For example if it's the first pupper run ever, the host is not enrolled in
+  # the domain yet and there is no Kerberos on this stage but it will 
+  # be when someone will actually try to read value from the Vault. At this 
+  # moment the actuall authentication would happen.
+  # Options for:
+  # proto       - protocol (http/htts)
+  # port        - port where vault server litens
+  # fqdn_expand - short hostname given, expend it
+  # auth_type   - if "external", use external command for authentication
+  # cmd         - command to run for the authentication. Should just return
+  #               tokn in the stdout. Should accept hostname + extra optional
+  #               arguments.
+  # args        - extra arguments for the command defined in the "cmd"
+  initialized = false
+  module RunCmd
+    module_function
+
+    # @param  [String] cmd   -> command to run
+    # @return [String]       -> Stdout
+    # @throws [RuntimeError] -> includes the Stderr
+
+    def cmd command
+      require 'open3'
+      stdout_str, stderr_str, status = Open3.capture3(command)
+      fail "#{command}: #{stderr_str.chomp}"  unless status.success?
+      stdout_str
+    end
+  end
+
   module Backend
     class Vault_backend
 
       def initialize()
+        Hiera.debug("[hiera-vault] backned is loaded")
+      end
+      def initialize_vault()
         require 'json'
         require 'vault'
-
+        require 'socket'
         @config = Config[:vault]
         @config[:mounts] ||= {}
         @config[:mounts][:generic] ||= ['secret']
@@ -26,10 +62,58 @@ def initialize()
         end
 
         begin
+
+          # Unless [:fqdn_expand] is set to 'false' we use the host name as it
+          # is. If it is set to 'true' we expand the name. This is used to 
+          # address correct Vault server from the cluster based on the DNS
+          # information. Might not be needed for all users, so if there is 
+          # no setting given nothing will happen. 
+          fqdn_expand = @config[:fqdn_expand] unless @config[:addr].nil?
+          if fqdn_expand
+            Hiera.debug("[hiera-vault] Expandin hostname #{short_hostname} to FQDN")
+            short_hostname = @config[:addr] unless @config[:addr].nil?
+            vault_hostname = Socket.gethostbyname(short_hostname).first 
+          else
+            vault_hostname = @config[:addr] unless @config[:addr].nil?
+          end
+          Hiera.debug("[hiera-vault] Vault hostname: #{vault_hostname}")
+
+          # We can have "expternal" authentication type:
+          # anything or absend -> default. Host and token are hardcoded 
+          # into the hiera.yaml
+          # "external" -> some external program returns access token string
+          # if no setting given, assume that authentication token is
+          # hardcoded in the hiera.yaml
+          auth_type = @config[:auth_type] unless @config[:auth_type].nil?
+          if auth_type == 'external'
+            Hiera.debug("[hiera-vault] Using external authentication")
+            token_cmd = @config[:cmd] unless @config[:cmd].nil?
+            token_cmd = token_cmd + " " + vault_hostname
+            if @config[:args]
+              token_cmd = token_cmd + " " + @config[:args]
+            end
+            Hiera.debug("[hiera-vault] Command: #{token_cmd}")
+            token_result = RunCmd::cmd(token_cmd)
+          else
+            Hiera.debug("[hiera-vault] Using hardcoded authentication")
+            token_result = @config[:token] unless @config[:token].nil?
+          end
+          port = @config[:port] unless @config[:port].nil?
           @vault = Vault::Client.new
           @vault.configure do |config|
-            config.address = @config[:addr] unless @config[:addr].nil?
-            config.token = @config[:token] unless @config[:token].nil?
+
+            # If we have "proto" in the config then we have new styled config
+            # in the other case just use the hostname + proto + port as is
+            # from the config. "Proto" is defining 443 in case of the https
+            # so it's more importnant then the "port".
+            proto = @config[:proto] unless @config[:proto].nil?
+            if proto
+              config.address = proto+vault_hostname+":"+port.to_s
+            else
+              config.address = vault_hostname
+            end
+            Hiera.debug("[hiera-vault] Will connect to: #{config.address}")
+            config.token = token_result
             config.ssl_pem_file = @config[:ssl_pem_file] unless @config[:ssl_pem_file].nil?
             config.ssl_verify = @config[:ssl_verify] unless @config[:ssl_verify].nil?
             config.ssl_ca_cert = @config[:ssl_ca_cert] if config.respond_to? :ssl_ca_cert
@@ -41,18 +125,23 @@ def initialize()
           Hiera.debug("[hiera-vault] Client configured to connect to #{@vault.address}")
         rescue Exception => e
           @vault = nil
-          Hiera.warn("[hiera-vault] Skipping backend. Configuration error: #{e}")
+          Hiera.warn("[hiera-vault] Vault configuration failed. Configuration error: #{e}")
         end
       end
 
       def lookup(key, scope, order_override, resolution_type)
+        # Here comes 1st actual attempt to authenticate against vault
+        # Ensuring we are doing this only once
+        if !@initialized
+          initialize_vault()
+          @initialized = true
+        end
         return nil if @vault.nil?
 
         Hiera.debug("[hiera-vault] Looking up #{key} in vault backend")
 
         answer = nil
         found = false
-
         # Only generic mounts supported so far
         @config[:mounts][:generic].each do |mount|
           path = Backend.parse_string(mount, scope, { 'key' => key })
@@ -112,8 +201,10 @@ def lookup_generic(key, scope)
           #Hiera.debug("[hiera-vault] Data: #{data}:#{data.class}")
 
           return Backend.parse_answer(data, scope)
-      end
+        end
 
+      end
     end
   end
-end
+
+