When I paste this into the jboss-cli prompt, I get this error:
 $ bin/jboss-cli.sh --connect
[standalone@localhost:9999 /] /subsystem=security/security-domain=GenericHeaderAuth/authentication=classic:add(login-modules= \
                                                    \
    {                                                                                           \
rg.jboss.security.auth.spi.RemoteHostTrustLoginModule",                     \
  \     "flag" => "required",                                                                  
        "module-options" => [                                                                   \
                          \ => "127.0.0.1"),                           
            ("roles" => "guest"),                                                               \
                                                  \
    }                                                                                           \
])

Operation 'add' does not expect any property.
[standalone@localhost:9999 /] 

I was able to get it to work using the string in my comment above though.