How to use jsonbuilder to make a json which has a key named like a DefaultGroovyMethods method (identity)?

def builder = new groovy.json.JsonBuilder()
        def root = builder.auth {
            identity {
                    methods (['password'])
                    password {
                        user {
                            name {
                                usrName
                                domain {
                                    id usrDomain
                                }
                                password "openstack"
                            }
                        }
                    }
                    scope {
                        project {
                            name prjName
                            domain {
                                id 'default'
                            }
                        }
                    }
                }
            }
        assert builder.toString() == '{"auth":{"identity":{"methods":["password"],"password": {"user":{"name":"admin","domain":{"id":"default"},"password":"openstack"}}},"scope":{"project":{"name":"admin","domain":{"id":"default"}}}}}'

assert output:

    Assertion failed: 

    assert builder.toString() == '{"auth":{"identity":{"methods":["password"],"password": {"user":{"name":"admin","domain":{"id":"default"},"password":"openstack"}}},"scope":{"project":{"name":"admin","domain":{"id":"default"}}}}}'
           |       |          |
           |       |          false
           |       '{"auth":{"methods":["password"],"password":{"user":{"name":{"domain":{"id":"Default"},"password":"openstack"}}},"scope":{"project":{"name":"admin","domain":{"id":"default"}}}}}'
           {"auth":{"methods":["password"],"password":{"user":{"name":{"domain":{"id":"Default"},"password":"openstack"}}},"scope":{"project":{"name":"admin","domain":{"id":"default"}}}}}

Basically the "identity" key is ignored. I have seen that there is a method called "identity" belonging to DefaultGroovyMethods, but I have no ideea how to overcome this. First time writing Groovy, have a little background in Python. Any help is apreciated!

Complete solution done with Szymon Stepniak's answer (and other corrections to json declaration):

def builder = new groovy.json.JsonBuilder()
    builder auth: [
            identity: {
                methods(['password'])
                password {
                    user {
                        name "$usrName"
                        domain {
                            id usrDomain
                        }
                        password "openstack"

                    }
                }
            },
            scope: {
                project {
                    name prjName
                    domain {
                        id 'default'
                        }
                    }
            }
                ]
    assert builder.toString() == '{"auth":{"identity":{"methods":["password"],"password":{"user":{"name":"admin","domain":{"id":"default"},"password":"openstack"}}},"scope":{"project":{"name":"admin","domain":{"id":"default"}}}}}'

Just in case someone wants to follow along this example.

To overcome this limitation (closure passed to JsonBuilder.call() method resolves identity method in the delegation chain), you will need to either represent your JSON document as a map or at least use a map up to identity key and from this place you can use a closure.

def builder = new groovy.json.JsonBuilder()

builder auth: [
    identity: {
        methods (['password'])
        password {
            user {
                name {
                    usrName
                    domain {
                        id usrDomain
                    }
                    password "openstack"
                }
            }
        }
        scope {
            project {
                name prjName
                domain {
                    id 'default'
                }
            }
        }
    }
]

Also, keep in mind that the closure you defined does not produce the expected JSON string, but it will have identity key that you are missing in the closure example.