Merge pull request #2324 from fluent/add-secret-to-tls_client_private…

…_key_passphrase

out_forward: Add secret to tls_client_private_key_passphrase

lib/fluent/plugin/out_forward.rb

@@ -102,7 +102,7 @@ class ConnectionClosedError < Error; end
     desc 'The client private key path for TLS.'
     config_param :tls_client_private_key_path, :string, default: nil
     desc 'The client private key passphrase for TLS.'
-    config_param :tls_client_private_key_passphrase, :string, default: nil
+    config_param :tls_client_private_key_passphrase, :string, default: nil, secret: true
 
     config_section :security, required: false, multi: false do
       desc 'The hostname'