vault:add and authentication=<x>:add have arguments of type OBJECT with a value-type of STRING. The arguments passed to the operations are complex-type, so the value-type should be containing the complex type description.

Examples:
/core-service=vault:add(vault-options=

{KEYSTORE_PASSWORD=>MASK-20OB41ZkH8YzlPTICpKg5.,KEYSTORE_ALIAS=>jboss,SALT=>12345678,ITERATION_COUNT=>50,ENC_FILE_DIR=>/path/to/enc/file}

)
/subsystem=security/security-domain=test/authentication=classic:add(login-modules=[{code=UsersRoles,flag=required,module-options={usersProperties=$\{jboss.server.config.dir\}/users.properties,rolesProperties=$\{jboss.server.config.dir\}/roles.properties}}]