The Dgraph password type is not query-able as a field. This is settable using the @secret directive on the type itself, where you can set a field and pred for the type. For example, if you set the Dgraph schema as:
password: password .
Then, in your GraphQL schema, you can use this predicate like so:
type User @secret(field: "userPassword", pred: "password") {
...
}