How to configure to use a ${xxx} predicate variable (like ${1} or ${remaining}) in the undertow expression filter with CLI and in standalone.xml configuration file

Issue

• How do I configure to use a ${xxx} predicate variable in the undertow expression filter with CLI or standalone(-*).xml configuration file? For example, I would like to use ${remaining} or ${1} like the following predicate:

  path-prefix('/foo') -> redirect('/foo-extra${remaining}')
  

  or

  regex(pattern="/user/(.*?)./.*", value=%U, full-match=true) and equals(%u, ${1})
  

• Adding an undertow expression filter with a value ${xxx} returns an error in CLI:

  /subsystem=undertow/configuration=filter/expression-filter=foo:add(expression="path-prefix('/foo') -> redirect('/foo-extra${remaining}')")
  {
      "outcome" => "failed",
      "failure-description" => "WFLYCTL0211: Cannot resolve expression 'XXXXX'",
      "rolled-back" => true
  }
  

  I tried escaping ${remaining} with \ (like \${remaining}) in CLI:

  /subsystem=undertow/configuration=filter/expression-filter=foo:add(expression="path-prefix('/foo') -> redirect('/foo-extra\${remaining}')")
  

  However, the above ${remaining} is expanded as a system property variable. So, it does not work as expected.

• Undertow predicates use the ${xxx} tag to access a value from the predicate context, but the expression is not valid for CLI or inside the standalone.xml or domain.xml file.